@dorney easier and stranger than it seems, lol
Is it important to sign up in every instance? I have no idea.
If I want to know my followers at once, what do I do? I dont know, I think the are developing this app.
Welcome!!
You're doing just fine so far. 
Here's an intro video for Mastodon:
https://www.youtube.com/watch?v=IPSbNdBmWKE
(the video was made four years ago, but it's a very good general intro)
And here's a page about this specific instance (qoto):
Welcome!
@dorney Yell into the cave, ignore your echo, and listen for a response 😀