Oh hey Crusher! Glad you decided to try mafia! Try reading the first post of the thread since there is where I explain how to play mafia, but I'll give you a little rundown.
Mafia is about two parties, the town and the mafiosos. The town have to get rid of the mafia and the mafiosos have to outnumber the town in order to win the game. To do that, every day people can cast a vote and whoever receives more votes will be executed. During night time, you can talk to other players trough PM's, and it's where you normally choose the skill you want to use (you don't choose the character who you want, you just get assigned one of the roles I made at random). That's the general idea, but if you have more questions then don't hesitate to ask.
Also, one of the moderators of the group, send him an invitation to join so he can get the notifications from the group.