Federation is not automatic. You can't make a new instance and automatically "see" all of the Fediverse from it; you need to create connections with it.
This is primarily done by following accounts from other instances. You'll see their toots and boosts, which will help you "see" more of the Fediverse.
Larger instances, like .ART or .social, see a lot of the Fediverse because they have thousands of users following tens of thousands of others, creating lots of inter-instance connections. 2/7