This post was very helpful for that: https://lemmy.world/post/266744
The same person has 2 other chapters that were very helpful for me. Check them out!
I'm in Kbin on my phone. If I open a post that was made in Lemmy and it looks like a community I want to follow, I scroll tk the bottom of the post. There should be the name of the Lemmy community with an icon, and underneath it a subscribe button. I just click on that to subscribe to that specific Lemmy community.