@docpop @AnneTheWriter1 I explain it like neighborhoods. Each instance is a neighborhood community, and your "home" instance is any neighborhood in which you have a residence (or your favorite one if you have multiple domiciles, if you like).

Just like cities contain many communities consisting of anything from apartments (i.e. Mastodon) to subdivisions (say, Akkoma) and with varying population densities (e.g. large instances might be like Manhattan, smaller instances might be like a small town), so too do many instances of various types of living spaces use the same "mail" service to communicate. And of course there are libraries (bookwyrm) and video stores (peertube).

ActivityPub is like the mail that allows you to communicate with other neighborhoods whether you live there or not, and you can also "return to sender" if you need to.

The local timelines are like your small neighborhood bulletin boards, the home timeline is like the city newspaper, and the federated timeline is like a firehose into the collective stream of consciousness of the entire fediverse.