As you prepare to make a good confession, you want to ask God's forgiveness for any way in which you have offended him but particularly for any serious sin. If you are not certain what you should bring to the priest in confession, do not be afraid to ask him for help. The priest is there to assist you and to share with you God's love and mercy.
Many people find the Ten Commandments to be a good frame of reference for an examination of conscience. The Commandments are listed here as a reminder that you might find helpful.
Act of Contrition
O, my God, I am heartily sorry for having offended you, 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 you, my God, who are all good and deserving of all my love. I firmly resolve with the help of your grace, to confess my sins, to do penance and to amend my life. Amen.
Original Sin is the sin committed by Adam and Eve, the first human beings. This sin was a willful act of disobedience, a rejection of God's command that was so devastating that it ruptured the relationship which our first parents enjoyed with God. As a result of this sin, paradise was lost to them and to their descendants until our Redeemer, Jesus Christ came to conquer sin and death and restore us to our inheritance of the Kingdom of God. Original sin taints all human beings and is washed away through the sacred waters of baptism. However, while original sin is removed, its effects remain. One of these effects is concupiscence, that disordered desire within us which produces an inclination to sin (1264, 1426, 2515).
Mortal Sin is defined by the Catechism of the Catholic Church as "a grave infraction of the law of God that destroys the divine life in the soul of the sinner (sanctifying grace), constituting a turning away from God. For a sin to be mortal, three conditions must be present: grave matter, full knowledge of the evil of the act, and full consent of the will" (1855, 1857). The Catechism emphasizes that "to choose deliberately - that is both knowing it and willing it - something gravely contrary to the divine law and to the ultimate end of man is to commit a mortal sin. This destroys in us the charity without which eternal (happiness) is impossible. Unrepented, mortal sins bring eternal death" (1874). This "eternal death" we call Hell, where those who have died unrepentant of mortal sin suffer the eternal separation from God and loss of eternal happiness, i.e., seeing God face-to-face.
Venial Sin, according to the Catechism, "does not destroy the divine life in the soul, as does mortal sin, though it diminishes and wounds it" (1855). Venial sin is a failure to observe necessary moderation, in lesser matters of the moral law, or in grave matters acting without full knowledge or complete consent" (1862). We must realize, however, that while venial sins do not have the grave effects of mortal sin, "deliberate and unrepented venial sin disposes of us little by little to commit a mortal sin" (1863). It should be the goal of every Christian to strive, through steadfast prayer, acts of penance and works of charity, for a life free of sin.