okay so you are SlyFox@lemmy.world, meaning your “home instance” is lemmy.world. When logging in it will first ask for instance, you provide it with that website.

then username is obvious, for you its just SlyFox

Then, for this place thing specifically it DMs a code to your lemmy account. So just log in on Lemmy.world and check your inbox for a message with your code. Then you should be in.