A - Thanks for the questions.
Thanks for thinking that we are a reliable source for Catholic teaching. But, remember not to give us 100% trust. That is for God and His Church alone. Thus, I always try to use primary documents of the Church in answering questions, when possible.
As for indulgences, here is what you need to know. I start with the Catechism's answer to the question, "What is an indulgence?"
1471 "An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints."The next logical question is what is temporal punishment?
"An indulgence is partial or plenary according as it removes either part or all of the temporal punishment due to sin." The faithful can gain indulgences for themselves or apply them to the dead.
Lucky us, the Catechism also answers this question (bold emphasis added).
1472 To understand this doctrine and practice of the Church, it is necessary to understand that sin has a double consequence. Grave sin deprives us of communion with God and therefore makes us incapable of eternal life, the privation of which is called the "eternal punishment" of sin. On the other hand every sin, even venial, entails an unhealthy attachment to creatures, which must be purified either here on earth, or after death in the state called Purgatory. This purification frees one from what is called the "temporal punishment" of sin. These two punishments must not be conceived of as a kind of vengeance inflicted by God from without, but as following from the very nature of sin. A conversion which proceeds from a fervent charity can attain the complete purification of the sinner in such a way that no punishment would remain.In other words, we still must be purified before we enter into heaven. If we are not made ready to enter into Heaven before we die, then the purification process will take place in Purgatory. This is why the Apostle John writes in Revelation 21:27 "nothing unclean will enter it (heaven)." We must be made clean to enter into Heaven.
1473 The forgiveness of sin and restoration of communion with God entail the remission of the eternal punishment of sin, but temporal punishment of sin remains. While patiently bearing sufferings and trials of all kinds and, when the day comes, serenely facing death, the Christian must strive to accept this temporal punishment of sin as a grace. He should strive by works of mercy and charity, as well as by prayer and the various practices of penance, to put off completely the "old man" and to put on the "new man."
The good thing is that we are all connected to The Body and Bride of Christ - the Church. Thus, every Christian is tied to every other Christian by all of us being united to Christ and His Church. We are blessed to lift others up by our deeds and prayers. This means we are able to help the souls in Purgatory or lessen our own temporal punishment, by tapping into the holiness of The Church and the storehouse of grace that is given access to us by the merits of Christ and the Saints. The Catechism says:
1478 An indulgence is obtained through the Church who, by virtue of the power of binding and loosing granted her by Christ Jesus, intervenes in favor of individual Christians and opens for them the treasury of the merits of Christ and the saints to obtain from the Father of mercies the remission of the temporal punishments due for their sins. Thus the Church does not want simply to come to the aid of these Christians, but also to spur them to works of devotion, penance, and charity.What a blessing! We can help those souls in Purgatory or obtain an indulgence for ourselves and lessen our purification needed. There are two kinds of indulgences - Plenary (all temporal punishment is remitted) and Partial.
1479 Since the faithful departed now being purified are also members of the same communion of saints, one way we can help them is to obtain indulgences for them, so that the temporal punishments due for their sins may be remitted.
Here is some additional reading:
*How To Get an Indulgence
*Handbook on Indulgences (aka - Enchiridion of Indulgences).
*Myths about Indulgences
I hope this helps.