If you know the address of an account on the Fediverse, you can make it appear within your own server so you can follow and interact with it:
1. Copy and paste the address into the search box on your server
2. A link to the account's profile will appear, click on it to interact
This works with all kinds of Fediverse addresses including Mastodon, Pixelfed, PeerTube, BookWyrm, Friendica, OwnCast etc.
This also works with a profile page's web address.
Find out more at https://fedi.tips/whats-my-accounts-address-how-do-i-follow-other-peoples-addresses-how-can-people-follow-my-address