It begins with the same lunge as a cartwheel. The arms are covering ears; weight of body is on lunge leg in front. The back leg is straight. Legs are as far apart as it is from the floor to your waist. You lever forward into a T or Lever position. As you tilt to the floor you do the airplane turn with your whole body. Your hands will contact the floor with arms by your ears, head turns to smell armpit of your favored side.
The distance from hands to front leg is the same as the distance from the floor to your waist. Your hands will be in one of three positions: T each other like car parked in garage, kissing each other (fingers facing each other) or both hands turned backwards. Your legs will come together shortly after vertical. If you have not driven your back leg up, using your glutes and hamstrings, the round off will have no power.
Any deviance from a straight line in any part of the round off will create a slow, inefficient round off. If our arms leave the ears the same problem occurs. Remember straight is great, no curves or angles in your body. The longer and lower the round off, the more explosive the third skill will be. Snap the legs under you for a long back handspring. Snap down legs behind you for height on a skill after the round off. This is basic to all back tumbling. Feet under you means you go back like a back handspring or a whip. Feet behind you in a tight hollow lean forward with arms by your ears gives a parabolic lift with lots of time for twisting and flipping. The difference in where your feet hit the floor after the round off is in the timing of the legs coming together. The later they come together the longer the round off so the height will be greater.