You spawn on the edge of the initial playable area with a torch, bandage and map at sunrise. Find loot as you make your way to the center of the map. The radiation moves closer to the center over time. Games with only a few players will last about 10 minutes whereas one with many will last about 17 minutes.
You can spectate while waiting for the next game. Custom buildings which are used are created by members of the community. You can create and submit your own builds from any Intoxicated Sandbox server.