Welcome to the guild! Basically what Rockatiel said, though there isn't really a posting limit in advanced. They just expect you to be really into developing your character and stuff. Which usually means writing a lot more than "He stabbed it with a sword"-- though some people do unfortunately interpret that as "must make this as long as possible" for some reason.
There isn't really an advanced casual section, but you'll see some roleplays in the casual section where the GM says they're doing "High Casual"-- which usually means they expect more.
Anyway, I think we could help you out better if you tell us what sort of thing you're into roleplay-wise?