Need a good (correct) explaination of deep squat

[Elementality]

Hey, Ive been squatting for a while but Im really trying to master it to its fullest potential. I go real deep now, and Im worried about my knees. Ive read your supposed to keep your knees over your toes in order to keep your back in correct form but it seems to me like it would put too much pressure on the knee joints. My questions go on and on...

Was wondering, anyone have a good previous thread, video, or any manual on how to deep squat correctly?