Graces and indulgences are two different things.
You will always get graces by praying. Graces come from God.
An indulgence is a separate benefit given by the Church, not by God directly. Indulgences reduce the temporal punishment for forgiven and absolved sins. In short, they reduce or make easier our Purgatory, or the Purgatory of another deceased person. You can earn an indulgence for yourself, and this is on top of any graces you get from God from your prayer activity. You can also earn an indulgence for a deceased soul in Purgatory, and still get the graces from God for yourself. Note that you can’t earn an indulgence for another person who is still living, but of course you can pray for them and God will help them.
I linked the current Manual of Indulgences above. It has been simplified a lot since 100 years ago, but it is still really complicated. So if you read it you might find it confusing. I’ll try later to find some good easy articles to post to you on indulgences. If it makes you feel any better, most Catholics, including many clergy, don’t understand indulgences very well either and some of them actively dislike indulgences as being too complicated, too legalistic, or reminding people of Martin Luther objecting to the “sale of indulgences” in the 1500s.
Many of us who regularly earn indulgences are doing it to pray for dead people, not ourselves. I personally think it’s pointless to earn indulgences for oneself, since if one prays habitually during one’s life, one will get a plenary indulgence automatically upon death even if the priest doesn’t show up in time to grant one via his Apostolic Pardon.