I've been hearing a lot about Mastodon for a while and thought I'd look around, see if I know anyone there, see what it's like, see if it seems to work better than Twitter... and the first step is to choose a host community/server, from dozens of options. The options are grouped into categories like "Tech" and "Arts" and "Activism" and there's also "General" and "Regional". None of the regional offerings are my region, so I browsed General and Tech.
All of the communities have names and short blurbs. Some sound serious and some sound less-so. Mastodon is a Twitter-like social network, so -- unlike topic-focused Q&A sites, subreddits, forums, etc -- one should expect people to bring their "whole selves". That is, a person on a tech server is likely to also post about food and hobbies and world events and cats. From the outside, I can't tell whether the mindset of the Mastodon-verse it "well yeah, duh, the server you choose is really just a loose starting point because you need to start somewhere" or if there's more of a presumption that you'll stay on-topic (more like Reddit than Twitter, for example).
A selling point of Mastodon is that it's distributed, not centrally-managed; anybody is free to set up an instance and set the rules for that instance. One considering options might reasonably want to know what those rules are -- how will this instance be moderated? But I see no links to such things. Many instances also require you to request access, which further deters the casually curious.
I guess the model is that you go where your friends are -- you know someone who knows someone who knows someone with a server and you join and you make connections from there. That's a valid and oft-used model, though I wasn't expecting it here.