A magazine is like a Reddit subreddit or Lemmy community.
A collection is a way to view multiple magazines in one feed. /c/Technology, for example, has a bunch of tech magazines. That way, you can view all the tech news in the fediverse without having to go to separate magazines.
I know everyone else has said these exact words, but glad that you're feeling better!
It's good to see that you're looking into delegating tasks. It's important for others to be able to pick things up whenever you're unavailable, unwell, or just exasperated. Alongside getting more instance admins, I'd also recommend getting other moderators on the magazines you own (e.g., /m/tech). The spam on those can get really bad, so there should be a few active magazine moderators to deal with those.