[Damion]

Squating requires full body strength and flexibility.

If your back and knees tell you to stop you have a strength or flexibility imbalance or possibly a flaw in your technique.

I would recomend having someone go over your form during some really low weight squats if you do it right i doubt it will hurt. then slowly over time add weight. All your leg pressing has strenghened a few of the primary movers but has done nothing for all the stabalizing, core muscles and balance needed to squat effectively. I used to be in the same boat leg press with 8 or 9 plates a side but i could not properly squat 1 plate a side.

It is very very common to see people use lots of weight on a leg press yet not be able to squat much. But anyone in the know will be far more impressed with full depth squats of two plates a side over a leg press of 7 or 8 a side.

As for the original post the internet can be a decent place to find out what you are doing but you will deffinatly need a personal trainer to show you how to do it properly machines need to be adjusted properly and free weights need to be used in a full safe range of motion.


Summary

Leg press = Ego lift

Squat = performance lift