Penitent: "Bless me Father for I have sinned. It has been __ months/days/years since my last confession and there are my sins....."
We must confess all grave/mortal sins in number and kind. For example: "I have purposely missed Sunday Mass 5 times."
Venial sins are not required to be confessed however it may be helpful for an individual to confess even venial sins that are struggled with in order to unburden themselves and receive advice.
After you've listed your sins the priest will give you a penance to say and you'll respond with the Act of Contrition after which the priest will pray the words of absolution to forgive your sins.
There are various resources on the web that can help you review your conscience
or better understand the sacrament