It gets easier, promise! You’re registered to the lemmy.world instance. You’re able to see all posts from all the other instances that are federated (kinda like you how you can see all subreddits that haven’t been shut down/set to private, even if you’re not subbed). There are a couple of instances that have been defederated for alt-right bollocks. I think sh.it.just.works might be one of them. If you’d like to see alt-right bollocks you can sign up directly with that instance.

The bottom line is that unless you have very niche interests, you don’t need to join any other instance other than lemmy.world. You’re here, you’re in, and you can see all the mainstream instances as well as all the different communities (subreddits) created on those instances.

I’d recommend checking out !newcommunities or !communities on the lemmy world instance to find and subscribe to the communities you’re interested in. Or you can all set your feed to “all” rather than “subscribed” and subscribe to anything you like from there. I hope that helps!