The Squat

The squat is known as the king of exercises. This is a fair call as it demands whole body strength and a good movement pattern. A lot of so called strong men don't need to squat and would rather use the squat rack for bicep curls or playing on a BOSU ball! This is why they will never be strong in the real world, so if something needs to be lifted there beach muscles will let them down every time.
A lot is said about core strength, will the BOSU guy have a strong core? Probably not, where as the squater will. Squating requires a very strong trunk, to maintain good lifting posture. This can be targeted more with other squat variations e.g front squats, Zerscher and one legged squats to name a few.
What about my knees! It is true the squat can stress the knees, generally though it is usually down to poor movement patterns, than anything else. The focus should be on the hips, and pulling your ass down, this reduces the load on the knees and maximise the contribution of the glutes (biggest muscles, we should use them!).
This will not only spare your knees, but add some weight to your lift!
Now not everybody should squat, if you have no cartilage or your knees are really banged up, you should consider some other options.
Once you have grooved a good movement get under the bar and crank them out!