So the idea with the Federation is there can be many communities with their own rules/main topics right?

If I'm interested in many things, let's say Red and Purple. Do I join both the Red and Purple mastodon instances (ie 2 accounts now)? Or do I join one and then use the federated timeline to see the other?

I've seen some great write-ups to explain Mastodon but this info would be useful for any non-technical person.