Confessing to a Catholic priest is not just a simple recitation of a laundry list of sins. Some preparation is necessary for this sacrament of reconciliation. You must know the number of times that you have committed specific grave sins. Furthermore, the Catholic Church teaches that, in order for a confession to be valid, the one confessing must feel genuine contrition for his sins and intend to change his ways.
Find out when confession is offered at a particular parish. While waiting outside the confessional, perform an examination of conscience. This entails determining what sins you have committed since your last confession. Use the Ten Commandments as a guide in finding out whether an action or thought was sinful. You must confess only your mortal sins in order to be forgiven. If you are afraid of forgetting your sins once you are in the confessional, write them down on a piece of paper.
Choose which way you will confess your sins after entering the confessional. Many parishes have partitions available for anonymous confessions but it is usually possible to step around the partition and confess face-to-face if this makes you more comfortable. You may want to know which options are available before you go to a particular parish.
Begin your confession by making the sign of the cross and saying "In the name of the Father, and of the Son and of the Holy Spirit. Then say, "Bless me, Father, for I have sinned." Then you will say how long it has been since your last confession. Continue by enumerating and describing the types of mortal sins you have committed since then. Finish by stating that you are sorry for your sins.
Listen as the priest counsels you regarding your sins and assigns your penance. He will ask you to say the Act of Contrition. He will listen as you recite it. When you are done, the priest will say the words of absolution. After he finishes, say "Thank you, Father" and exit the confessional.
Complete your assigned penance. This is typically a certain number of specific types of prayers or readings from Scripture. Completing penance is part of the process of this sacrament.
Remember that the priest is there to help you. If you forget how to proceed, ask for help in the confessional. The priest will be able to guide you through the process.