So… to answer the first question: as I said in a different response recently, questions are just questions. They might be asked out of ignorance, curiosity or malice, but the question itself should never be considered stupid.

As for what lemmy.world is: it’s an online service managed by a small group of people that enables users, and users of other lemmy servers that have an agreement with it, to post information in sub-forums, which can be up and downvoted by the users of the forum community; those votes and their effects can be managed based on the rules of the specific community.

Nostupidquestions@lemmy.world is one community; I’m part of it, even though I’m not a member of lemmy.world, but of lemmy.ca, which is federated with lemmy.world. This means that when I access/post content on lemmy.ca, that gets shared across to the other lemmy servers like yours that hosts or carries the communities I’m involved in.

So… single platform, multiple instances, which have different peering agreements with each other to federate content.

To complicate things further, Lemmy is part of the Fediverse, a larger group of online services that share the same federation structure and much of the same network code, but are designed for different purposes. Lemmy is similar to Reddit, Mastodon is similar to Twitter (ability to broadcast short messages that go into subscriber’s feeds and get aggregated), there’s one specifically for sharing video with others, etc.

This only tangentially answers your questions, but I felt like it was a good idea to get the foundation concepts out of the way first, after which others can reply to the particular bullet points.