In basic gymnastics, we'd always start off with learning things solid on the ground. In order to achieve higher level gymnastics, you have to firmly understand the basic positions. For instance, a forward roll or a backwards roll.
The backwards roll is very simple. You would tighten up in your stomach and hollow out your back and make it round. You want to get as round as possible, just like a soccer ball or something, to roll over. Very simple. You would put your hands up like you're holding pizzas up. Your head would go underneath, nose down your belly. And as you roll back, as soon as you sit down, you need to aggressively lift your knees over your head and put your hands on the floor and push. This simulates a backwards flip in the air. Same exact motion, same exact positioning.
The backwards roll, though, is dangerous. You definitely don't want to lift your head up. And if you lift your head up, then you're going to end up hitting your head on the floor, obviously causing a little bit of a headache. Easiest way to do this, very simple. Get a little momentum by standing up first, squat down. And then kind of push back, keeping your head in. And then just kick those feet over your head.