The Backward roll
Here is a brief video on how to on the backward roll in Jiu Jitsu. Remember how important is to learn how to fall without getting injured, that is why I recommend you to learn and practice this technique.
It is important to protect your head, neck, and spine while doing this, that is why you roll diagonally from right shoulder to left hip and from left shoulder to right hip. This is a technique you can use while training, not really recommended to use it in competition because once you turn your back to your opponent this can go to your neck and apply a choke.