I have students come to me all the time with doctors notes that say so and so has strained their knee and cannot squat for 2 weeks. My standard response is, "Did you ask your Dr. how to take a dump? Because without squatting, that is going to be messy." I am, of course, joking but it hammers home the point that without the ability to squat many of lifes' daily functions become much more difficult. The other common knock against squatting is that it is bad for the knees. I often hear I can't squat, I have bad knees. My response, "You have bad knees, because you don't squat." I will concede that squatting incorrectly could eventually be harmful to the knees, but a correctly performed squat does not hurt the knee it actually makes the whole knee complex stronger. Lets take a look at how to perform a perfect squat.
Start with the feet. They should be a little bit wider than your shoulders with your feet turned out slightly. From here you let instinct take over. I use a toilet analogy a lot because everyone can relate. Imagine you are about to sit on the toilet you will naturally start the downward motion by internally rotating the pelvis, and flexing the hips. This is mumbo jumbo for pushing your hips back. Here is a picture of the starting position.
And here is the internal rotation and flexion of the hip. This is the correct way to start a squat. Note that there is little to no movement of the knees.
For whatever reason, if you are not thinking about the toilet and I ask you to squat most people will start the squat by bending the knees forward. Like this
Once you have gotten the hang of starting the squat with the hips and not the knees. Continue to push your hips back and down. As you are doing this you want to check to be sure that your knees are tracking out over top of your toes and not caving in inside of them.
The above picture is a good start but is still an immature squat. Many people get stuck at this point because of flexibility issues. A mature squat is one where the crease of the hip is below the crease of the knee as in the picture below.
A few points of performance to look for when performing the squat.
Hips back and down
weight on your heels the whole time
Stomach and lower back tight
Get up off of your duff right now and see if you can perform a perfect squat.