Lemmy.world is not like the main lemmy website. There isn't one. It's just the biggest instance. That's all. Hilariouschaos.com like many others are just smaller ones.
For example, are all instances and will have duplicated communities. They can all have a memes community and so forth.
Think of instances are just independent websites that either agree or disagree to connect with other and share eachothers content and access to eachothers communities.