This is a bad quality clip (poor light and no sound) but it does show a huge transformation from the Early Standing Exercises clip.
At the beginning, I am stood balancing lightly on my fingertips. My body is straight and all the muscles around my lower back, hips and pelvis are straight (not bent and unable to fully straighten as they were previously). And I am quite comfortable just standing, not feeling like I'm going to fall back under my own weight and strain.
Then I stand & sit (which I do loads of). This strengthens the leg muscles and helps build the muscle mass around bum and thighs. In the beginning, this exercise was all arms, and the strain made it hard to keep going, but now you can see that the legs and pelvis are helping at the end of each push up, and the shoulders stay fairly relaxed.
I find that I'll always get a few more out of each set if I say out loud to myself "push" or "legs" on each push up. It helps remind me that I want the legs to work and not the arms on this one. More legs equals less pain, and that is a good motivation!