While working out, it is very important to maintain proper posture or else there are chances of hurting yourself.... Yes, you need to be not only careful but also get your posture right to get the maximum benefit...while doing squats never put pressure on your knees... To get the form right use a chair.... Lower your body without bending the knees, as you do while sitting on the chair, do not bend... Practice this with a chair and also check the you tube videos to get a better hold... Once you understand it, then you can practice it without the chair.

Take care