As it seems you are mostly having trouble with the section types, I'll go over them quick.

[b]Free[/b]
In free, you can expect to find one liners. I do not know much more about the place.

[b]Casual[/b]
Casual is the den of posts with usually couple paragraphs of content and some modicum of character development.

[b]Advanced[/b]
Anything that is beyond casual, really. Sometimes it goes near the character limit of a post, sometimes less is more, but still rarely under three paragraphs a piece. Character development and compelling storytelling are pretty much a must.

[b]Arena[/b]
A fight? Count me in! This place has characters fight each other. Power levels and the attention to detail varies.

[b]Nation[/b]
For the emperor! Here people play as whole nations, usually in war against each other AFAIK.

[b]Tabletop[/b]
Tabletop roleplaying games through a forum. Simple as that.

[b]1x1[/b]
RPs with only two participants. Lots of romance and outright smut here. 18+ content should be played out via PM.

I hope I have been of assistance!