To be honest you don't need to create an account on another instance. It's a little complicated, but that's what I understood:
Each instance it's a website (and I'll use website instead of instance from this point forward, but you can read instance). You can create an account and login to that website.
All the websites talk the same language, so from inside one website you can explore another, as if it was the same.
Your account, on one website, is valid on the other websites.
Search on a "community finder" website. I'm using Lemmy Explorer (mark the "Show NSFW" option).
Use a client that can search communities on the fediverse, instead of searching only your instance. I found wefwef is the best for exploration, but it's poor on the text editing side. I'm using Jerboa to reply to you right now.