Right, Right, Right, where do i start? Well every horse can jump whether is a Shetland, or a 18hh horse. You have to gradually train it but you cant have a beginner or a person who doesn't know what her/him is doing. Really you need to have special help if it is your first horse or whatever. If you know your self then go ahead, But why would you put this question on here if you already knew your self? Right so.... You want to know how you jump a horse? Well all you do is start from the basics which is lunging, walking, handling and caring for your horse/pony. Once you have built up a bond with your horse/pony that's when it comes to jumping.
First of all start jumping the horse without a person on its back. Then gradually build up to the point where (the human being, person knows how to jump and so does the horse) i would advise you to try it on another horse which is used to learners and will jump with some one their back at the smallest of heights. If you haven't got a clue about horses and you have gone and got a youngster, which you are breaking in and teaching the basics
Once you are now working on the horses back, then just walk, trot and do the basic stuff. If its the first time for the horse to jump then walk the horse of the jump at the height of a pole. If its you learning to jump, then have someone in the field to supervise you and help you.
if you want to know how to actually jump on the horses back then here we go:
when you jump (on the horses back) then you might have seen the showjumping position. all you do is look through its ears and go with the horse. Push your self forward, but not to forward other wise you wont be on the horse after its finished the jump. If you don't know this, then go to have lessons, find a trainer or some one who can help.