Check out Becoming a Supple Leopard and it will give you the basic squat technique. There are positional issues with really good explanations and if you have mobility limitations it will tell you exactly what you need to do for it.
Not every person on earth is going to end up looking exactly like Kelly when he squats no matter how much time they spend mobilizing. If it hurts your knees to have your feet that straight then turn them out a little. We have been very clear at MWOD there is a window between straight ahead and about 15 degrees of turnout where you can still get the most hip strength and power. The important part is don’t let your feet collapse and or ankles collapse in. Focus hard on that and just squat as deep as you can. Surely look over the book and work on limitations in the ankle and the hip but don’t also get caught up in wanting to look exactly like someone else.