I signed up for TTRPG network, not realizing I also can access Lemmy through it! To be honest I don't know a lot about how the fediverse works at all but so far I like what I'm seeing. Reminds me of reddit circa 2009. In fact, I think this is going to replace my use of Reddit altogether, as it definitely serves the purpose of providing endless content to scroll to.
Treat it like email, except emails are public(posts) and your instance can block sending and reciving emails from another instance. You are not required to create a new email with that instance to interact with a post unless that server has blocked your instance.
E.g someome with gmail is free to message people using yahoo, outlook, proton, but may block some domains (e.g spam domains)
This is very cool because a lot of online forums were completely gutted when Facebook took over, and seeing communities adopt the fediverse is awesome.