The front squat is a basic strength exercise in weightlifting, and one of the most commonly used exercises other than the competition lifts.
Place the barbell in the clean rack position. Place your feet between hip and shoulder width with the toes turned out so that at full depth each thigh and the corresponding foot are in line with each other. Set your back in a complete arch, take in a large breath, and lock it in, forcefully tightening all trunk musculature. Bend at the knees and hips simultaneously to move down as directly as possible into the bottom of the squat with an upright posture, maintaining tension on the legs throughout the movement. Full depth is achieved when the knees are closed as much as possible without losing the arch in the back (if you cannot sit into a full depth squat, you need to work on mobility). Upon reaching the bottom position, immediately transition and stand as aggressively as possible, again with the knees and hips together to maintain your upright posture—try to lead the movement with your head and shoulders. Use the elasticity of the bounce in the bottom of the squat to help transition and drive back up as quickly as possible.
For a lot more information on the execution of the front squat, and squat in general, see the following articles:
The front squat is a leg strength building exercise very specific to the clean, but also will help the jerk by emphasizing quad strength, and improve the ability of lifters to pull from the floor with upright posture. It is also an effective trunk and back (particularly mid and upper back) strengthening exercise. It is usually used in combination with the back squat for weightlifting.
There are a huge number of possibilities when it comes to programming the front squat. Most commonly weightlifters will use sets of 1-5 reps, but more often 1-3 reps. Weights can be very heavy to maximal for strength development, or more moderate for training speed, timing and position for the clean.