Squats are probably the best exercise for lower body. Apart from quads,hamsting and glutes squatting also workout the core abdominal muscles. They help build strength and stamina of the entire body.
But squatting comes with its own risks. A wrong posture can result in serious back pain and injuries..
Follow the below steps for attaining a proper posture while squatting-
1. The squat rod should be placed at shoulder height.
2. Position yourself under the rod so that it rests on your traps and shoulders.
3. Lift the bar off the rack grabbing it with a wide grip.
4. Keep the feet shoulder width apart with knees slightly bent.
5. Now go down bending from the hips as if you sitting on a chair.
6. Keep going down till the thighs are parallel to the ground.
7. Now push back. 
Remember to exhale while pushing up and inhale while going down. Make sure you do not arch round your back.
If you are beginner start with light weights and try attaining a better posture before moving onto heavier weights. Note the heavier the weights in squats the more effective it gets.


So what are you waiting for...Shut-up and squat :)...