Depending on what your host has made available, you will be playing the game on a Quest 2, 3S, or 3. All three devices have a full-color 4k screen for viewing the game.
The Quest 3 variants have full-color passthrough cameras to see the real world
The Quest 2 only has black and white passthrough cameras. So the real-world lobby will be in black-and-white but the game will still be in full-color.

The headset's lenses focus your eyes as if you're looking into the distance.
If you wear glasses for distance, you should still wear them in the headset.
If you wear glasses for reading, you won't need them. Pull back on the headset's strap and push the headset straight onto your face.
Pull the strap down over your head and make sure it is secured around the curve of your head. If your headset has a hard strap, tighten it via a twist knob in the back. If your headset has a fabric strap, pull apart the plastic tabs to tighten it, or push them together to loosen it. If you need to adjust the top strap, you can pull up on the Velcro, slide it to the right length, and secure the Velcro again. The Quest 2 has a power button on the right side of the headset.
The Quest 3 variants' power button is on the left.
If the screen isn't already on, press the power button to turn it on. If the view feels out of focus, you may need to adjust the lens spacing:
The Quest 3 has a wheel on the bottom that gradually adjusts the spacing. The Quest 2 and 3S have only 3 settings. You'll instead grab one of the lenses to slide them into position.
The controllers are custom-built for left or right hands such that the middle finger can comfortably press the grip button and the pointer finger can comfortably pull the trigger. This game does not require both hands. If you are unable to use one of the controllers, you can leave it behind.

Remember to use the straps to keep the controllers from flying out of your hands. Wrist straps with a little slider are the default, but some grips may have knuckle straps that adjust with Velcro or bungees.

From the main menu, select Join. You will be auto-connected to the game. Your host will have placed at least one pair of calibration points in the space (though they can add several).
They will be numbered 1 and 2. While touching the first calibration point of any pair with either controller, press A, B, X, or Y on that controller. Then proceed to the second calibration point and do the same. If you are adjusting your headset later and accidentally put it to sleep by bumping the power button, it may lose track of its place in the room. If at any point you notice the game is misaligned, you can hit the left menu button, select Recalibrate and tap any 2 calibration points again to get back to the game. Once you're calibrated, you should be able to see the virtual lobby environment as well as the other players, clad in virtual armor. As a group in the lobby, you can select from the maps and game modes your host has made available via the settings table. If you would like to update your display name or your color, you can do so from the customization stations. Once everyone has joined and the settings have been selected, hit Ready to start the game. Once the game has started, you cannot join or rejoin the game until the other players have returned to the lobby. If it's a team game, team buttons will appear. Hit the button corresponding to the team you want to join.
When the last player joins a team, you will have 10 seconds before the teams are finalized. After that point, there is no switching teams. When the spawn points appear, step into a point to join the game.
More than one person can be in a spawn point at a time.

Your objective varies by game mode:

In Deathmatch, you get a point each time you kill another player. In Capture the Flag, you get a point each time you bring the other team's flag (which looks like a floppy disk) from their base back over to your base. Adventure Mode has all players working together as a team exploring a bigger map and completing objectives. There are quite a few details that can be customized within the game mode. Check the Rules Panel to see detailed instructions for the current settings.

Press and hold the middle finger grip button on either hand to equip your gun. Pull the trigger with your pointer finger to fire the gun. If you see a weapon drop floating in the game, you can grip to pick it up and use a different weapon. To switch back to your basic pistol, reach your hand behind your head and grip.
You can do this again to switch back to your new weapon. While your gun is in one hand, grip the other hand to equip your shield. There is also an option from the in-game menu to enable a mounted shield. The mounted shield will hold itself wherever you drag it and it can be toggled with the A or X button. As you take on damage, your armor glow will start to fade until finally, you die. When you die in the game, you will be sent to the spawn world. You will be invisible to other players during this time but will show up as a blinking bumper if they get too close.
Don't walk into the blinking bumpers. The spawn world is transparent so you have some extra help to avoid collisions while you're invisible.

Spawn points will appear after a brief cooldown period. Step into any point to return to the game.

If you come across a turret, you can grip one or both handles to activate it. Pull the handles in the opposite direction you want to aim (like it's connected by a pivot in the middle). Pull and hold the trigger on either gripped hand to fire the turret. The turret has powered rotation. If you pull far enough right or left, it will rotate to keep aiming. If you get motion sick easily, you might want to turn that off with the button on top before you board. There are also gondolas and elevators in some of the levels that will carry you between floors or over gaps. These are activated by a button push. A few of the maps have stairs. When you step onto stairs in the game, the stairs above and below you lower and rise to match the stair you're standing on. Simply walk along the stairs as if you're on flat ground. This will be unnerving at first... It helps to look at your feet. After the game you can review the score, start a rematch, or return to the lobby.

Each player will need a Meta Quest 2, 3S, or 3 headset and a copy of the game.
Catastrophic Inversion playtesters regularly use each of these headsets and they all work great for the game. All three devices have a full-color 4k screen for viewing the game.
Quest 3 variants have full-color passthrough cameras to see the real world
The Quest 2 only has black and white passthrough cameras. So the real-world lobby will be in black-and-white but the game will still be in full-color.

You'll need a big space.

Currently, all maps are fixed sizes.
Most of them are 24 x 14 meters (79 x 46 feet) or the size of a basketball court.
We also have maps that are half-court (10 x 10 meters / 33 x 33 feet) but we can't fit as much fun stuff into those, so it's a huge improvement if you can find a full court to play on. Look around. There may be a space available to reserve at a local school, community center, or church.

If you don't have any such space available, you can play in standing/roomscale mode at home.

You will need a decent Wi-Fi connection throughout the whole space.
The game does not require internet access, but the devices need to connect over a local network connection.
Hopefully there's already a good connection at your space and you don't need to worry about this, but if there's not, you can bring along a home router or two for a stronger signal.

There's nothing special about our setup, but as an example:
We have two of these ASUS routers (that have been on sale for $50 or less) that do a Wi-Fi 6 mesh network. We put them about 1/3 of the way along opposite walls and that works great. If your router is completely offline, the game will work but the headsets won't connect automatically since they can't detect the internet, so you'll need to manually connect to the Wi-Fi each time they are turned on.

Sometimes setting the connection as Metered in the Wi-fi Settings can make it test network connectivity less frequently and it might assume it's connected even when it's not. This works best if you are able to connect the routers to the internet at home and have each headset connect successfully there.

If the building has Wi-Fi, but it's a weak signal that doesn't work well for the game, you could try this $30 wifi bridge we have used.
It also helps if your network requires individual registration for connected devices.

How it Works

Plug the device into one of your router's LAN ports. Navigate to the device's local address. Use its online interface to connect to the Wi-Fi network of the venue and register if needed.
If it came down to it and you needed to, you could probably connect the device to your phone's hotspot. Make sure the headsets are set to a metered connection though so you don't have a fleet of headsets updating over your phone's data plan.

Plug it into your router's WAN port, and now it will pass through the internet to your router. All the devices on your router will now connect to the internet through this bridge, passing connectivity tests.

The network connection for the game will still happen over your local network on the router.

If there are just a few players or if you're playing alone, one of the headsets could host the game.

If there are more players or you want to put a spectator feed up on a TV, you can host the game using the PC version on Steam.

There are a few options in the Settings menu we should review. You can set a headset to Guest Mode, turning off the host button on the title screen and avoiding confusion for new guests.

There are also some options for helping catch cases where the headset has come unaligned (which can possibly happen if the headset is removed or put to sleep). We have these set to our recommended values, but feel free to adjust as needed.

Check For Headset Centerpoint is a setting to help with Boundaryless Mode. By default, the game enables Boundaryless Mode, which turns off the Guardian Boundary (which limits your space to 10 x 10 meters / 33 x 33 feet). In favor of our in-game calibration system made for larger spaces.

Even with this enabled, Meta still provides annoying pop-ups when you've travelled 20m or so from the headset's origin point. The best place for the origin point is the center of your real space, but it defaults to the location you turned on the headset.

If you store the headsets along the middle of one of the long sides of the space, that may be close enough to the center to avoid these messages. You'd then set the Centerpoint check to After Calibrating, where it will only bug the player about the centerpoint if it isn't close enough by our estimations. If that's not possible in your space, you can reset the origin point by leaving the game, creating a guardian boundary in the middle of the space, and re-joining.
You would then set the Centerpoint check to Before Calibrating so they can see the centerpoint every time and move if needed.

If you are playing in a particularly large space or have to store your headsets farther away, these pop-ups may be unavoidable. They don't generally cause any major issues beyond an annoyance, so you can just close them and keep on playing, or you can completely eliminate them by fully disabling Physical Space Features through developer mode.
If you do this, you will want to set the centerpoint check to Disabled.

About Developer Mode & Disabling Physical Space Features

Putting your headset in Developer Mode allows a few features that you couldn't previously do, including: sideloading apps from unofficial stores, modding existing apps, and manually disabling the Guardian Boundary.
Anyone can put their headset in Developer Mode. You do not have to be a developer. (You do need to create a placeholder development studio in Meta Quest, but it's not a lengthy process.)
You can follow these instructions on the Meta Website.

Once your headset is in Developer Mode, you can disable the boundary by going to the Settings App > Developer Settings > Disable Physical Space Features.

Once Physical Space Features are disabled they will be disabled in ALL games. You will not get a warning that they aren't enabled when starting other games, which could result in a collision. You will need to remember to manually re-enable them when you stop playing Catastrophic Inversion.

You will want to find at least two convenient spots in the space to use as Calibration Points. (Though you may have several sets if desired.)
Each pair will be most accurate if they are a few meters apart and at least 6 inches different in height.
You can use anything that works for you, but feel free to use these ones we made. The game will walk you through setting up the space, having you:

Touch each corner to measure the space; and Touch Your Calibration Points to align later without touching the corners. After the initial setup, the other players will only need to touch the calibration points to line up the game.

In addition, all participants will receive a copy of the space mapping on any game they join, so they can host a game in the same space later.

As long as your points don't move, your space mapping is usable indefinitely.

When you're ready to host, you need to tell it how space will be handled. You can choose between playing Together in Large Space, Separate In Small Spaces, or a Large Space game that allows Separate, Small-Space players to join. There's also an option for easy transfer of a space mapping from a headset to a PC (since you need a VR device to map the space).

Once you're hosting a game, you will have some options for setting it up: By default, it will broadcast the game's info across your local network allowing any other copy of the game to auto-discover your session and easily connect. You can turn this off to require participants to know your IP address to join.
Some enterprise networks block this kind of broadcast but most will still generally allow you to connect manually by IP.

If your device has a public IP or you have set up port forwarding on your router, you can host the game online.
Customized instructions for that are available in the same menu.

This menu also lets you determine what maps are available to the guests. If your space is big enough for the full-court maps, the half-court maps disable themselves automatically, saving guests from unwittingly picking a small, less interesting map... but you can re-enable them here if you really want to use them.

This menu also allows you to create and save customized game mode presets. You can also set what presets are available to your guests. It defaults to a demo mode where only 4 basic game modes are available with the same time limit, (which you can set as the host).
You can switch it to let them pick between all presets, or only your custom presets.

For advanced players, you can activate a customization console in the VR environment and they can set the individual settings themselves.

Things move a lot quicker if your guests know what they're doing.
If you want to make sure your guests are trained up ahead of time, you can send them the link to the how-to page, which has videos and written instructions: https://toastidwaffel.com/cihow2#play

Alternatively or additionally, you can put up this printout, which they can scan to take them to the instructions.