I am currently using Lemmy.zip through the app voyager.
I can also see content from other places like hexbear and fedinsfw.
If I login to lemmy.zip on a desktop I can use my voyager credentials. But I am only able to view lemmy.world and nothing else here.
If I login to fedinsfw on desktop I can seemingly access a multitude of places such as I can on voyager, including lemmy.zip.
I’m sorry if this is such a dumb thing to get confused about. I’ve heard explanation for what all this is, but I’m still just not quite sure I understand.
Each instance is run by a different team, often based in different countries and jurisdictions. Day to day, the main differences will be around content policies (moderation, how openly federated it is)
It’s like picking between different email providers, just that all have more or less the same features.
We have these guides too
https://fedecan.ca/en/guide/get-started
https://fedecan.ca/en/guide/threadiverse/detailed-overview