No need to feel dumb, the way BBCode works does sometimes feel like it's able to break when you don't expect it. Other than IsaacOscar's link (& the generic forum BBCode info), I can only recommend trial and error with the preview I'm afraid. One thing that helped me figure stuff out is the "reply with quote" option - if I see someone's post using a thing I was looking for, I can quote it to see the proper BBCode for it.
Ah, I see. I've grown used to adding most of them manually, as the automatic placement didn't always work as expected. And it looks like neighbouring blocks of spoilers need three empty lines, that seems to be working for me:
quote