"Bless me, Father, for I have sinned. My last confession was _________. These are my sins..."
Then tell your sins, asking questions if needed. Use only the amount of detail necessary for the confessor to understand the gravity of the sin.
All mortal sins must be confessed according to number and kind in order to make a good confession. It is also beneficial to confess venial sins.
In order to receive forgiveness, you must be sorry for your sins, not knowingly withold any sins, and firmly intend not to sin again.
When you have listed your sins, finish by saying:"I am sorry for these and all the sins of my past life."
The confessor may then give you some words of advice before giving you a penance to perform (often prayers or acts of charity). Then he will invite you to say an Act of Contrition.
Examples of an Act of Contrition:
"Lord Jesus, Son of God, have mercy on me a sinner."
OR
"O my God, I am heartily sorry for having offended Thee and I detest all my sins because I dread the loss of heaven and the pains of hell but most of all because they offend Thee, my God, who art all good and deserving of all my love. I firmly resolve, with the help of Thy grace, to confess my sins, to do penance and to amend my life. Amen."
Following the Act of Contrition, the priest gives absolution for your sins to which you respond "Amen" and then he will say a prayer of dismissal.
After exiting the confessional, you should take time in church to say a prayer of thanksgiving and any prayers given as a penance before departing.