Say 'start' to start exploring. you will start at level 0 aka "The Lobby" sometime, you will randomly noclip to level 1 or "Habitable Zone". often, you might find entities such as a smiler, hound, frowner, bacteria, skin stealer, or a partygoer. then level 2 is "Pipe Dreams" and there are technically infinite levels meaning this game wont stop. Make sure to be safe and explore. alot of times you might start running out if sanity, but luckily, you might find "Almond Water".