Few exercises can set off heated arguments from a mere discussion, and squats
are one of them.
The back squat is one of the 3 competition lifts in powerlifting, which also include the deadlift
and bench press.
The back squat is one of the most difficult and rewarding exercises you can
perform in a weight room. If performed properly barbell back squats are not only
a great exercise for the legs, but also the glutes, lower back, and core.
Since
back squats put a lot of compressive forces on the lumbar spine and require full
energy stores to get the most benefit, they should be performed at the beginning
of your workout.
More about the Correct Form of Back Squats
You could write a 100 page instructional guide about squat form but as long
as you know the basics you can benefit from squats while staying injury free.
The most basic form tips for squats are as follows:
Sit back into the squat (slight anterior pelvic tilt before you bend
your knees)
Keep your back tight & in neutral alignment
Keep your knees in line with your toes
Keep your knees from traveling forward past your toes
Keep your weight off your toes
There are exceptions to these general form tips for advanced sqatters but for
the most part, if you keep your form tight by following the previous tips, you
will stay injury free and be able to get the most benefit from squats. It is
also important to consider, that whether or not you can use impeccable squat
form is largely going to depend on your muscle balance. If you cannot keep
proper alignment, excessively arch your back, experience pain in your shoulders,
etc. you should go back to the drawing board and fix what is wrong with corrective stretches,
strengthening weak accessory muscles or whatever.
Safety Considerations with Barbell Back Squats
If there is a single exercise that you should use a weight belt for squats
are it. This is especially the case if you are using heavy weights. Contrary to
popular belief, a weight belt does not "support the back" directly. What a
weight belt does is create an artificially strong core by pressing against the
abdominal cavity. This also increases intra-abdominal pressure and together your
artificially strong core is what supports your lower back. Even with a weight
belt, you can easily get injured while performing squats. As a rule of thumb, if
anything doesn't feel right, and we're not talking about general muscle fatigue
stop and rack the weight, figure out what is wrong and either try again or move
on to another exercise.
Few exercises can set off heated arguments from a mere discussion, and squats
are one of them. 
