If you want to practice back-hopping first try and stay on yor back wheel for as long as possible, do this by riding forwards at walking pace, and pulling the front brake to do a little endo, then as your back wheel reaproaches the ground shift your weight backwards and you will go back on your rear wheel. Trust your brake basically and just balance on the back wheel for as long as possible then take it from there, theres loads of topics on here aswell so have a search and lots of ways of learning but thats how i did it.