The best way to start squats is to train your muscles to know the proper position of a squat. The best way to do this is with a chair. As I demonstrate in the video below, stand in front of a stationary chair and practice sitting back into the chair. As you will see, my movement is back, not down. 

As you progress you won't need to use the chair. Simply stand in a room away from any furniture and move backwards like you are going to sit in an imaginary chair. It's important to keep your knees from moving in front of your toes, which may cause some lower back injury if done improperly. 

Once you have the exercise down, incorporate it into your workout (or start a new workout routine). Build your way up to three sets of 20 squats with a 30-second break in between each set.