I have discussed the Catholic doctrine of indulgences (yes, Catholicism still teaches indulgences [many, even to this day, still think that the Council of Trent “got rid of indulgences”; instead, all it did was curb the abuses thereof]):
William J. Cogan, in a catechism for adult converts to Catholicism, wrote the following about indulgences (Lesson 26: “Indulgences”) which does a good job at (1) explaining the doctrine of indulgences and (2) the two forms of indulgences in a clear, succinct manner, so I am reproducing it here (also in the hope both errant Catholics and Latter-day Saints will not skirt this important doctrinal difference [Note: The term “Poor Souls” refers to the faithful who died with venial sins on their soul and are currently in Purgatory]):
1. Can all your sins be forgiven in Confession?
Yes, if you are truly sorry for them.
“If we confess our sins, he is faithful and just, to forgive us our sins, and to cleanse us from all iniquity.” (1 John 1:9)
2. In Confession is all the punishment due to your sins taken away?
1) In Confession the eternal punishment (Hell) is taken away
2) all the temporal punishment is not always taken away.
3. What is meant by “temporal punishment”?
“Temporal punishment” means that, even though all your sins are forgiven in Confession, God still demands that you be punished (for a time) either in this life or in Purgatory.
4. What is an indulgence?
An indulgence is the taking away of all or part of the temporal punishment still due to sin.
5. How do indulgences take away temporal punishment?
The Church has the authority from Jesus Christ to draw on the spiritual treasury made up of the merits of Christ, His Mother and the Saints.
“Whatsoever though shalt loose on earth, it shall be loosed also in heaven.” (Matthew 16:19)
6. What do you have to do to gain an indulgence?
You have to—
1) have no mortal sin on your soul;
2) say the prayer or do the work to which the indulgence is attached;
3) have the intention of gaining the indulgence, and
4) fulfill all the conditions laid down by the Church for each indulgence.
7. How many kinds of indulgences are there?
Two kinds: plenary and partial.
8. What is a plenary indulgence?
One that takes away all the temporal punishment due to sin.
Examples: saying the Rosary before the Blessed Sacrament, making the Way of the Cross, attending Forty Hours Devotion, reading the Bible as spiritual reading for at least half an hour. A Person can gain only one plenary indulgence per day, except in danger of death, when he may gain a second one.
9. What else is required to gain a plenary indulgence?
1) Confession (at least within several days)
2) Communion (preferably on the same day you perform the indulgenced prayer or work)
3) Prayer for the Holy Father’s intentions (at least one Our Father and one Hail Mary);
4) Having no attachment in your heart to sin.
10. What is a partial indulgence?
One that takes away only part of the temporal punishment.
Examples: using holy water, medals or statues that have been blessed, reciting the Litany of the Blessed Virgin Mary.
11. Can you gain an indulgence for someone else?
Yes, for the souls in purgatory only.
The month of November is dedicated to the souls in Purgatory. During this month, Catholics are especially urged to gain indulgences for the Poor Souls to impress on them the importance of praying for the Poor Souls at all times.
12. Can temporal punishment be taken away by any other means?
Yes, the Sacraments of Extreme Unction takes away all temporal punishment due to your sins, if you receive it with perfect intentions. Plus, any prayer of good work done in the state of grace takes away some temporal punishment, but indulgences take away more. (William J. Cogan, A Brief Catechism for Adults: A Complete Handbook on How to be a Good Catholics [Chicago: ACTA Foundation, 1951; repr., Rockford, Ill.: Tan Books, 1993], 95-7, emphasis in original)
William Jenkins, a traditionalist Catholic priest, has a video discussing this doctrine using Voga's book as a basis for his comments (while Jenkins seems to be a Sedevacantist, a "mainstream Catholic" will take very little exception to his comments on indulgences, only his "shots" against Francis):