A backside grind is basically just a frontside variation done by coming at the curb or rail you are going to grind and grinding on it while facing the opposite direction you would be facing if you were doing a frontside. To learn how to do a backside grind, you first have to be comfortable doing a frontside and being able to do a 180 helps, but not necessary. You have to come at what you are going to grind as if you are going to do a frontside, but when you are at the place where you are going to slide, you have to jump at the curb like you were going to do a frontside, but as you jump you need to turn your body so that your skates will land with the grind in between your 2nd and 3rd wheel, with your back facing whatever you are grinding. This trick isn't much harder than a frontside, it just takes a little practice for your body to learn what it feels like to grind backwards. This trick is easiest to learn on a curb or low bike rack. An easy variation you can do with this trick is a frontside to backside or a backside to frontside.