Penance requires . . . the sinner to endure all things willingly, be contrite of heart, confess with the lips, and practice complete humility and fruitful satisfaction. (CCC 1450) 

First, the penitent should act with a contrite heart. Contrition is “sorrow of the soul and detestation for the sin committed, together with the resolution not to sin again. When it arises from a love by which God is loved above all else, contrition is called “perfect” (i.e. the contrition of charity). Such contrition remits venial sins; it also obtains forgiveness of mortal sins if it includes the firm resolution to have recourse to sacramental confession as soon as possible. (CCC 1451-1452) 

Second act of a penitent is the confession of sins. Through such an admission, the penitent looks squarely at the sins he/she is guilty of, takes responsibility for them, and thereby opens him/herself again to God and to the communion of the Church in order to make a new future possible. (CCC 1455) 

The third act is a humble satisfaction. Many sins wrong our neighbor. One must do what is possible in order to repair the harm (e.g., return stolen goods, restore the reputation of someone slandered, pay compensation for injuries). But, sin also injures and weakens the sinner him/herself, as well as his/her relationships with God and neighbor. Absolution takes away sin, but it does not remedy all the disorders sin has caused. Raised up from sin, the sinner must still recover his full spiritual health by doing something more to make amends for the sin: he/she must “make satisfaction for” or “expiate” his/her sins. This satisfaction is also called penance. (CCC 1459) It can consist of prayer, an offering, works of mercy, service of neighbor, voluntary self-denial, sacrifices, and above all the patient acceptance of the cross we must bear. Such penances help configure us to Christ, who alone expiated our sins once for all. (CCC 1460) 

Reconciliation with God is thus the purpose and effect of this sacrament. For those who receive the sacrament of Penance with contrite heart and religious disposition, reconciliation is usually followed by peace and serenity of conscience with strong spiritual consolation. Indeed, the sacrament of Reconciliation with God brings about a true “spiritual resurrection,” restoration of the dignity and blessings of the life of the children of God, of which the most precious is friendship with God. (CCC 1468)