Squat

Performance

1. Set up the squat rack so the bar is slightly below shoulder level.

2. When you're ready, duck under the bar and grip it widely with your palms facing forward. Rest
    the bar on your upper back, not your neck!

3. Place your feet slightly wider than a shoulder width apart, with your toes pointing slightly    
    outwards.

4.  Hinge your hips and push your butt backwards until your hamstrings are parallel with the floor.

5. Keep your chest up, your shoulders back and your eyes looking straight ahead.
    Remember to keep your back straight, this is especially important when you are squatting with            heavy weights.

6.  Push out of the squat with your heels, don't let your knees cave in towards the center.

Muscles

The involved muscles are: Gluteus Maximus, Quadriceps, Hamstrings.

Also the important core muscles get some focus: Erector Spinae, Transverse Abdominus, Gluteus Medius/Minimus, Adductors, Soleus, Gastrocnemius.