Cardinal O'Malley, in explaining the Portiuncula Indulgence, which is August 2, gives us a good anecdote in explaining indulgences.
"I want to mention something about indulgences, which are often misunderstood. Indulgences are not forgiveness for sin but forgiveness for temporal punishment due to sin.
I like to explain it to people with the following story:
As a child, once I came home very late for dinner. My mother was very upset, and seeing how upset she was, I felt very repentant and I told her that it would never happen again. She told me she forgave me, but as my punishment I would have to do the dishes.
So there was repentance and forgiveness, but there was still punishment.
But, as I started doing the dishes, my nana came in and said, “I will help you.”
That is an indulgence."
And I think I should start paying more attention to indulgences!