I've learned that to do squats safely, you have to keep the back in a vertical line so the pressure is shared, and not stressed on each backbone (by leaning foward). I also know that you gotta keep knees not past the toes. That's the easy part, but not leaning forward is hard for me. Are you supposed to learn to balance bending 90 degrres and keep your upper body back? cause that's like sitting back on a chair except you dont have a chair, so it's almost impossible.