It would probably be helpful to go to a couple of open shows, get a copy of the class schedule and just watch what they do. Pay attention to how the horses are ridden/presented and what attire is required.
Qtrbel had the basic facts.
Pleasure judges the horse, Horsemanship judges the rider.
Halter judges the horse, Showmanship judges the handler.
Local open shows are a great place to start. Many riders only show at these events.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger