Mafia is a game of the uninformed majority versus the informed minority. To elaborate, the game is divided into two teams: the Town and the Mafia. Mafia know who each other are, and can coordinate their actions privately. Town players on the other hand don't know anything other than their own role. To compensate, there are many more Town than Mafia. The objective of the game is for Town to eliminate by killing or lynching all the Mafia before it is too late. The game is divided into repeating phases of Day and Night. Day revolves around voting for a player to be lynched. Night is reserved for the Mafia to make their kills and certain players to use their special abilities.
Be warned - Mafia requires a time commitment. This generally depends on the player, but at minimum 30 minutes a day of solid effort is required. As part of the time commitment, Mafia requires a great deal of reading. Most people are actually quite poor at reading comprehension and playing Mafia is a great way to improve your reading ability, as well as your writing and ability to think and argue logically.