We sing in four parts - soprano, alto, tenor and bass. If you have sung before, you may already know which vocal group you are best suited to. If not, a basic guide might be to consider how high or low your speaking voice is. For example, a woman with a higher speaking voice may well be a soprano.
You don't have to know before you come - the best way is to come along and try it out - you'll soon find out what part is most comfortable for you to sing.