Just FYI to anyone passes by: I'm three weeks into Mastodon and loving it. The whole "fediverse" concept is cool and solves a lot of the problems Twitter (and Facebook)
have had (strikethrough there because I terminated my Twitter account and I haven't used Facebook in almost three weeks).
Mastodon is not a service. It's a software package anyone can use and run on a server of their own. A Mastodon server is called "an instance." An instance can connect via the internet to others, allowing anyone on any of them to follow and be followed by anyone else. It works rather well, which each instance having its own local culture and policies. To follow someone on another instance you need to know their full Mastodon identity, but that's no harder than knowing an email address. Mine, for example, is this:
You can use that to follow me from any Mastdon instance that is part of the same federation of systems (which, as far as I can tell, is any of the ones you might want to choose to use, unless you are a racist gun-nut, which means you'll likely use an instance that is connected to other instances with people, uh... such as yourself).
I do believe the decentralized, local-culture/global-connectivity model Mastodon uses represents the future. This may be a real turning point in the history of mass social media.