It can be a bit challenging at first. If you randomized mafia you know who your teammates are. Your goal is to blend in with the crowd and slowly kill off the civilians. If you're a civilian you have no idea what role anyone has except yourself. Your goal is to try and figure out who's blending in. If you think someone is acting funny or their story doesn't add up you might want to consider voting for them. You gotta be careful though because civilians can vote off other civilians. The game finishes when the mafia reaches parity, or if the civilians kill off the mafia team.