tapping on the horse shoulder ; smacking on the rump

Question
hello sir, sorry for asking horse racing question. please dont ignore it. this is regarding basic riding :

sir, when should a rider taps with the whip on the horse shoulder ; and when does the rider smacks with the whip on the horse rump. what does the horse learn from both these actions?

Answer
Tapping on the shoulder tends to "move or push" the shoulder away. It is more for just teaching the horse to move it's shoulder in the desired direction. It can also be used to teach the horse to move out or begin to take steps. Using a crop on the rump is to lengthen the stride. This will in turn result in a faster horse (theoretically).