Clips 1 & 2 show just a couple of incorrect ways to squat that are going to offer little to no benefit whatsoever.
Clip 3 is a box squat, a great way to build confidence and technique before progressing on to a full squat.
Clip 4 is how to perform a Bodyweight squat correctly:
feet shoulder width
weight distributed between mid foot and heel
chest and head up
neutral spine throughout (back not rounded)
Get these right, then start adding weight to the movement!