St. Theresa of the Child Jesus
You don't hear about indulgences anymore, at least not in Catholic circles. If it could be said that at one time they were over emphasized, it's surely true that today they're under-emphasized. Many Catholics simply don't know what indulgences are, and they're at a loss to explain the Church's position on indulgences when challenged by fundamentalists. And fundamentalists do bring up indulgences, perhaps because they know even less about them than the average, poorly-informed Catholic.
There is surely no better place to turn than to the Enchiridion of Indulgences. "Enchiridion" means "handbook," and the Enchiridion of Indulgences is the Church's official handbook on what indulgences are and which specific acts and prayers carry indulgences.
An indulgence is defined as "the remission before God of the temporal punishment due for sins already forgiven as far as their guilt is concerned." The first thing to note is that forgiveness of a sin is separate from punishment for the sin. Through sacramental confession we obtain forgiveness, but we aren't let off the hook as far as punishment goes.
Indulgences are two kinds: partial and plenary: A partial indulgence removes part of the temporal punishment due for sins. A plenary indulgence removes all of it. This punishment may come either in this life, in the form of various sufferings, or in the next life, in purgatory. What we don't get rid of here - we suffer there.
A partial indulgence, granted to the faithful who, at least with a contrite heart, pray to the merciful Lord Jesus a legitimately approved invocation. [e.g. Jesus I trust in You; My Jesus mercy; or any other approved invocation]