Squat (holding on)
Start in a standing position with your feet about shoulder width apart or a little wider. Toes should be pointed straight ahead or turned out somewhat. In this variation, you should hold on to something stable, ideally around waist level. That way, you can use your arms for stability/support, although you still want to use your legs as much as possible
Begin by lowering your hips back and towards the ground. The key is to make sure you move your hips back as far as possible during the descent, instead of your knees moving forward. Your knees might move forward a little, but the less they move forward, the less stress on the knees. Another important point is to keep your hips, knees, ankles, and toes aligned as much as possible. You should ideally be able to draw a straight line between these joints.
Finally, the movement should be slow and controlled (no bouncing at the bottom) and your heels should stay on the ground throughout the squat. These technique tips are the difference between an effective lower body strengthening exercise and a knee damaging exercise. For added benefit, you can actively tighten your glutes as you are standing up from the bottom position. Perform 15 reps of the exercise and breathe out while you are standing up.
If the exercise is too difficult or you have any discomfort at the bottom position, decrease your range of motion so you stay in pain free range. Another option is to hold a bent-knee position instead of moving up and down. This helps strengthen the muscles necessary to perform the exercise with movement.