Why do we want indulgences and how can we earn them?

The Catholic Norms on Indulgences define an indulgence as, “the remission before God of the temporal punishment due to sins already forgiven as far as their guilt is concerned.” So, after we confess our sins and are forgiven, we still owe temporal punishment due to those sins.
What does that mean?
It’s kind of like when the neighbor kid is playing baseball next door and ends up breaking your window. He can come apologize for breaking the window, and you can forgive him, but someone still has to pay to have the window fixed.
So, we owe reparations for the effects of our sins. Our sins not only damage the relationship we have with God, which He is always willing to forgive, but they also hurt our relationship with others and injure the entire body of Christ.
We pay for these reparations in two ways. First, when we die, if we die in a state of grace but are not ready for heaven, we will spend “time” in purgatory. Purgatory is the place where we make reparations for our sins and prepare ourselves for heaven. Some say purgatory burns like hell. It’s both a burning of desire to be with God, to have that beatific vision, and a burning of purification. Of course, we will want to be with Jesus, so we want to spend as little “time” in purgatory as possible.
That’s where indulgences come in. The second way to pay for all the windows we’ve broken by our sins is through indulgences. We can earn indulgences for ourselves or for souls in purgatory, but we cannot apply them to other living people. So how can we earn them?
There are many ways to earn indulgences, here are just a few:
• Adoration of the Most Blessed Sacrament
• Reading of Sacred Scripture
• Praying the Stations of the Cross
• Praying the Rosary
• Papal Blessing
• Visiting a Cemetery and Praying for the Dead the First Week of November
(Sources: Catholic Straight Answers, Catholic Norms on
Indulgences)

Read more in the “Why Do We Do That?” series from Deacon Mike Fritz.