I'm not sure if I can post here. Lemmy seems kind of complicated. For instance, I tried to post something and it said I can't because I'm on a local instance. So how do I find out what instance a community is on and how do I make it so I can post?
To summarize what others have said: You did manage to post. However, a moderator removed it, because you broke rule #1 of the community you posted to (which is that a post in !nostupidquestions@lemmy.world must contain a question).
The part of the message mentioning local user is that lemmy.world users get automatically notified when their posts on lemmy.world are removed. It has nothing to do with the reason your post disappeared. The usual behaviour is that you don't get informed when a moderator locks or removes your post, it just happens silently.
Don't feel bad about it, you're just learning. For better chances of success, make sure to read the community rules in the sidebar before posting.
On desktop web, the sidebar with rules is on the right. On mobile web, click the sidebar button:
You weren't necessarily on the wrong instance, it was just a (possibly confusingly worded) message informing you of your recourse if you believe the post was removed in error.
You can feel free to join another instance, you won't miss the bulk of the content here thanks to federation.