You need 100 schips to play in mafia. I think the next maifa game has started already though, so you'll have to wait till the next one starts. So, start saving up those chips and go read through some of the older mafia games to learn how to play. And you can play in the next game.
Mafia 5 has already started. It started yesterday I believe. Mafia 6 will start sometime after 5 has finished. However long that'll take I don't know. Sometimes mafia is over in a week or sometimes in takes a month you'll just have to wait and see.