I joined lemmy.world, because that’s the first one I came across. But now I can see the posts from many instances using voyager and Memmy. Now you can go and join any instance with interest you. That’s the beauty of it.

This explains the fediverse with some examples of different instances

https://socialhub.activitypub.rocks/t/introduction-to-activitypub/508

Try Zoho mail