Answer:
It depends what you want to advertise. In your own forum (your equestrian centre forum), you can advertise anything you like. In the gameplay forum you can ask any question about how to play the game. In the Equestrian centre classifieds forum you can advertise your equestrian centres need for a groom (for example) or that you are offering yourself as a groom. In the classified ads forum (under sales) you can advertise any horse that you are putting up for sale or a type of horse that you want.
I hope this helps!