In an ELI5-type answer: "Practicing" gratitude involves actively noticing your feelings of appreciation for something good in your life. That something good may be a meal, a relationship, overcoming an challenge, etc.
For an adult beginner a gratitude journal is a great place to start! You can purchase one, like the "6-Minute Journal" or you can grab a blank piece of paper and pick a prompt from this pdf[1]. Pick a prompt: "Something beautiful I saw today..." "A fun experience I had..." "Someone I admire.." and spend a few minutes writing about that. Write in your journal 2-3 times a week. That's it!
[1]: https://www.therapistaid.com/worksheets/gratitude-journal
I didn't come up with this and obviously cannot say if it would work for you. Look up "Three Good Things" if you're curious about the theory.
Sure, I agree. There is a lot of good in my life.
What seems to cause dissonance is how my life still feels like shit, despite all those good things. The answer I most often hear to this is "well, if you practiced more gratitude, you'd appreciate those things" - which feels like the old religious cliche of "if God doesn't help you, you aren't praying/believing enough".
But to ask a concrete question - how would you describe the "activity" of practicing gratitude to, say, a child who's never heard of such a phrase? Is it just the act of pointing out "good" things about your life to yourself, or is there anything more to it?