This is a good explanation I think. Unfortunately, it seems to be exactly the way I understood it before I asked.

It still doesn’t quite make sense.

How do I find other @peertube platforms? Is there a directory? When I try to sub to a channel, I’m prompted to download a messaging app?

It just isn’t intuitive. I’m a pretty tech savvy fella. I’ve now watched 3 videos on the topic, read the welcome guides, visited all the profiles looking for answers. But… I come up blank.