To get your back handspring first you have to have a solid back walkover . To start, in your back handspring you have to jump backwards ( as far as possible) and then push of with your hands then just put your feet. ( not too close because then you will have a hard time staying up because the force will push you backwards and not to far because you have a hard time getting up after you push off ) always do it medium ( just right right.)
A skill you could do to get your back handspring:
Put a tall mat about two inches lower than your size and keep on jumping backwards to
the mat until you know how to jump really far .Remember before you try try it with a spotter ( a person that will help you with your skill and makes sure you do not fall.)