Dear Julie,
When you make your first Confession depends on whether you have already been baptized or not. If you have not been baptized, then the sacrament of Baptism will free you of your sins and you will simply receive your first Holy Communon after making a profession of faith and receiving the sacrament of Confirmation. If you have already been baptized, then you will need to go to Confession for the first time. In this case, you are not expected to remember every sin you ever committted. But you are exprected to give some idea of the sins you have committed over the years. The priest will help you. You are in our prayers. Welcome!
Fr. Vincent Serpa, O.P.