If you’ve been on the Internet a long time, good analogies seem to be like email servers or (back in the day) Usenet servers. There can be lots of servers, and you get an account on one, but then you can post and read between all the servers. Like being on gmail but emailing people and reading emails from their accounts at other places. Or back in the day, like being on your ISP or university’s Usenet server, but reading posts from other servers and posting things people on other servers can read.
If you’ve been on the Internet a long time, good analogies seem to be like email servers or (back in the day) Usenet servers. There can be lots of servers, and you get an account on one, but then you can post and read between all the servers. Like being on gmail but emailing people and reading emails from their accounts at other places. Or back in the day, like being on your ISP or university’s Usenet server, but reading posts from other servers and posting things people on other servers can read.