call your nearest parish, find out the times of confessions, get there early to pray and think about what you are going to say, and reflect on the sins of your past life. Or you can talk to the priest directly and make an appointment.
when you get in to see the priest tell him Father, I have not been here for 10 years, and I don’t know how to do this, but I am sorry for all my sins. He will guide you from there. Then tell your sins, listen to any counsel the priests gives you, receive absolution, make an act of contrition – if you don’t have one printed from a prayer book, just tell God you are sorry and that you will do your best not to do these sins again. The priest will give you a penance, which you do as soon as you leave the confessional. Then you kneel down and rejoice quietly and thank God for the immense grace He has just given you.