Dear Moira,
A general confession is one in which one reviews his life and confesses all the sins he can remember. It’s a good thing to do at certain key moments in one’s life ( before one’s wedding or entering a novitiate, etc.). It’s usually a good idea to make an appointment with a priest before hand. You wouldn’t want to take that much time while a line of people is waiting outside the confessional.
Fr. Vincent Serpa, O.P.