The fediverse is a universe where many small social servers connect by exchanging letters under a shared set of manners. The name of those manners is ActivityPub. Mastodon, Misskey, and this museum town's hollo and hackers.pub all speak the same manners.
To start, you only need three words. actor (one resident's calling card — this is your account), inbox (that person's mailbox), and outbox (the file copy of the letters they've sent). The rest you'll pick up as you walk.
When you press "post" in the Mastodon app on your phone, the app asks hollo's reception: "Send this out for me."
Your post becomes a parcel in the shared tongue called Note, and the act of "I made this" becomes the verb Create. The dictionary of that shared tongue is the Vocabulary Sutra Repository.
From a follower's address like "@friend@mastodon.social", you look up the real address (its URL) in the directory. That's the Webfinger Gate.
You stamp a signature on the letter — so the receiver can confirm it really was sent by you and wasn't altered along the way.
The letter isn't thrown out right away. It's handed first to a storehouse (a queue) — so that even if the other island is away, it can be redelivered later.
The ship's true form is just an HTTPS POST. It carries the JSON letter to the URL of the other party's inbox (their mailbox).
The main hall of the other island examines the wax seal and copies the letter into its ledger. Your post appears on a follower's timeline from this copy.
That's all of it. What's inside the fediverse is a directory of addresses, signed letters, and mailboxes — and the craft of doing that carefully, hundreds of millions of times over, is what fills room after room of this museum town.
Even if you wander into a difficult room, you'll be fine reading just the one line under "If you're new here" and moving on to the next. The lens at the bottom right of the map — save it for last. It reveals the Hidden Town of Mathematics beneath the floor of the engineering town.