http://forums.graalonline.com/forums...19&postcount=1
This forum post should explain it very shortly and good.
But to sum it up and answer your questions.
Q: Everything listed on this hiring forum is actually hiring?
A: No, you have to look if there is some open application. Right now there are none but I'm writing some for Graal Kingdoms. So shouldn't take too long until you finde some.
Q: What are the requirements for every subject?
A: This can be different from subject to subject. The specific ones will be posted by each moderator of the forums. But I'm quite sure that one requirement will be the specific gold subscription for the subject. e.G. Kingdoms Gold for Graal Kingdoms. Playerworld Gold or Classic for Classic worlds etc.