I know this is a lot to take in, but think of it this way:

What if you could follow Instagram and Twitch and YouTube accounts from within Twitter?

Well, that's exactly how the Fediverse works! Different platforms are open to each other instead of being closed off as "walled gardens".

It's not competition, it's co-operation. When one platform's userbase grows, so does the userbase of all the other platforms.

The video shared in an earlier post is exactly about this:

https://framatube.org/w/9dRFC6Ya11NCVeYKn8ZhiD