Without a bar and some weight on your back, it is difficult to demonstrate proper technique. The body plus bar equals a system, and without the bar the system will be out of balance. What you are doing in this video is practicing poor technique; your back is rounding terribly (you are not staying tight), you are shoving your hips back to initiate the descent without pushing your knees forward.....
You are not going to learn the form first without weight on the bar.