This following diagram explains what is demonstrated in the video:
The rear foot and theform a line, which aims at the centre (spine in most cases) of the opponent. The hand/elbow and the same through the opponent’s structure form the lever arm. By bringing the lever towards the line, energy shoots towards the opponent. Note that there are two applied forces, one is used to push towards the , and the other is pushed towards the line. The two forces are created by two different parts of the body. While the lever is squeezed towards the line, the (and the line) cannot be moved (tossed).
In the video, different fixed points are selected as well, e.g. rear kua, middle of the trunk, front kua.