Since you didn’t quite get an answer, an “instance” is like a “website” kind of. Just like you’d go to Reddit and have access to all of the subreddits on their servers, an instance is a one version of Reddit. There are multiple “Reddits” like lemmy.world, lemm.ee, feddit.de, etc that all have their own “subreddits”. They all interact with each other though so you can see every community on every instance as long as they’re still linked.
“Reinventing “ the wheel should really come when you understand the wheel and it’s pros/cons and the problem your facing can’t quite be solved with the current tools.
If you can’t come up with good reasons on why something should be different, then you’re just looking to waste time and effort to say you’re different.