From the Catechism:
1459 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). Simple justice requires as much. But sin also injures and weakens the sinner himself, as well as his 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 must “make satisfaction for” or “expiate” his sins. This satisfaction is also called “penance.”
1460 The penance the confessor imposes must take into account the penitent’s personal situation and must seek his spiritual good. It must correspond as far as possible with the gravity and nature of the sins committed. 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. They allow us to become co-heirs with the risen Christ, “provided we suffer with him.”
The satisfaction that we make for our sins, however, is not so much ours as though it were not done through Jesus Christ. We who can do nothing ourselves, as if just by ourselves, can do all things with the cooperation of “him who strengthens” us. Thus man has nothing of which to boast, but all our boasting is in Christ . . . in whom we make satisfaction by bringing forth “fruits that befit repentance.” These fruits have their efficacy from him, by him they are offered to the Father, and through him they are accepted by the Father.
Also from the Catechism:
Forms of Penance (1434)
Interior penance is best expressed externally in three forms:
*]Toward oneself by fasting
*]Toward God by prayer
*]Toward our neighbor by almsgiving
There also should be tears, reconciliation with others, concern for other’s salvation, intercession of the saints, and charity “which covers a multitude of sins” (1 Pet 4:8).
We also see in the general grants of indulgences, four forms:
Raising the mind to God with humble trust while performing one’s duties and bearing life’s difficulties, and adding, at least mentally, some pious invocation.
Devoting oneself or one’s goods compassionately in a spirit of faith to the service of one’s brothers and sisters in need.
Freely abstaining in a spirit of penance from something licit and pleasant.
Freely giving open witness to one’s faith before others in particular circumstances of everyday life.
*[size=3]**I. Conceditur indulgentia partialis christifideli qui, in officiis suis gerendis et vitae aerumnis tolerandis, animum ad Deum humili fiducia erexerit, addita, etiam tantum mente, pia aliqua invocatione.***3
**II. **[/size]*[size=3][size=3][FONT=Times][size=3]Conceditur indulgentia partialis christifideli qui, spiritu fidei ductus, in servitium fratrum necessitate laborantium, se ipsum vel bona sua misericordi animo impenderit.[/size][/size]*19
[/FONT][/size]*[size=3][size=3][FONT=Times][size=3][FONT=Times][size=3]III. Conceditur indulgentia partialis christifideli qui a re licita et sibi grata, in spiritu paenitentiae, sponte abstinuerit.[/size][/size][/size]*38
IV. [/FONT][/FONT][/size]*[size=3][size=3][FONT=Times][size=3][FONT=Times][size=3][size=3][FONT=Times][size=3]Conceditur indulgentia partialis christifideli qui apertum testimonium fidei coram aliis, in pecularibus quotidianae vitae adiunctis, sponte reddiderit.[/size][/size][/size][/size][/size]*
A gift from God.:D