Earlier quoted context omitted.
People keep using email as the prime example of federation, but email is pretty terrible! I can't communicate with anyone whose address I don't already know. There's no real "discoverability." Many people have multiple email addresses, and I don't know whether I'm communicating with the correct one, or even whether more exist that I don't know about. If an email address stops working, it just... stops working. Emails…
Browsing the federated timeline, searching by hashtag and looking at who other people you know are following is the discoveability mechanism. Unlike Twitter, ActivityPub sites generally don't beat you over the head with follow recommendations. The goal is not to get you mentally addicted to spending hours a day on Social Media.
A Google search is probably the most common discovery mechanism. Once people start putting their Mastodon addresses on their web pages, it will start getting easier.