I'd be glad to tell you all about it. ^^ So, mafia is a game where there are two to three groups. Each group is against each other. Now, the main two groups are the Townies and the Mafia. Sometimes they have like a third party where they win when either the mafia or townies win, or vigilante, where it's one person who has powers like the mafia but is on it's own. So, the mafia have a power to "night kill", which is, In the night period of the game, their group votes to kill one of the townies. In the day period, everyone (townies, third party, vig, mafia...) discusses and votes for who they think is scummiest. By the way, the townies don't know who anyone is, they don't know who their fellow townies are or the mafia or anybody. The mafia know who the mafai are who are not mafia. And the vigilante only knows who he/she is. So, at the end of the day period there is a vote tally and the person with the most votes gets ki8lled off and their role is revealed. There are basic town roles such as Cop (who can investigate in the night period and find out if one person is mafia) and a doctor (who can choose to save someone who they think is going to get killed by the mafia. They aren't allowed to know). And that's the basics of mafia. The game I'm hosting has a theme though, and it's FMAB.
Although I suggest that if you havent played mafia online or in real before, you should play the beginner game first.