Irrationally unsure about what Conversations are on the forums

I know I'm just being irrational. I know people will make fun of me for asking this. I know. I know. I know.

But still.
What are Conversations on the forums? (I already have a guess that they are private chats with individuals, but if I guessed wrong and clicked the button anyway, I'd never forgive myself)

Another thing. If conversations are what I think they are, when is it acceptable to start one?
Oh, also, what's up with people putting all their art behind spoilers? This is just a bit of confusion on my part, I've already asked about it, and I know it's probably about convenience, but, once again, irrationally unsure. (I just want to know if I should do it for my art)

 

Conversations are private chats between 2 or more users. They're also used for staff applications to inform you if one has been accepted or denied.

People put art behind spoilers for two reasons:
1) if the art might contain upsetting content (blood, injuries, horror elements), in which case the spoiler is usually marked to state this
2) if it's an art dump, as images take up a lot of space on a post, so putting them in spoilers allows someone to easily skip over stuff they aren't interested in & just overall navigate the page better.