If your knees hurt when you're squatting down and trying to come back up to stand, there's a really easy way to fix that.
It's keeping the shins vertical when you go to spot so letting your hips drop back, instead of letting your knees go forward.
When your knees go forward, that causes a lot of friction and pain on the back of the kneecap. Dropping the hips back is super important but it feels crazy awkward.
An easy way to practice is to use a chair that will slide easily on the floor. You're going to position your knees or shins right up against the seat of the chair, your feet about shoulder-width apart (usually it's as wide as the chair will let you put your feet on the inside of the chair legs), then you're going to drop your hips back and come back up to stand. This is just a little mini squat.
If you start to drop your hips back and the chair goes forward then you know that you messed up.
If you can do these little mini squats 10 times at the top of the hour every hour, in just a couple of days your body will start to feel more natural dropping your hips back instead of to moving your knees forward.