hello, comprehesive guide:

the game starts automatically, you move with arrows, kill imposters with space and get in doors marked with the green arrow with down arrow key

every time you enter a door time resets / you go to the past and there are your past selves and additionally +1 impostor (with each loop) that you should identify and murder before going to past again

but be careful don't murder yourself or get murdered by your past selves

that's it, I wish it was more clear, since it's you against you the game is pretty sandboxy

have fun!