"You have closed registrations on mastodon.social, so how will my friends get in or find me?"
Tell your friends to sign up on https://knzk.me/about then tell them: "Search for MyUsername@mastodon.social" and voilà, you have found each other.
It's very similar to how e-mail addresses work.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!