There is a program used by the earlier generations of bodybuilders (by earlier I mean pre-steroid era) called Squats Milk. Do a search for in-depth information on the prorgam, but I’ll give you the breakdown here.

You start your workout (after warmup) with 20 deep-breathing squats. Your weight for this is your 10 rep max, and you take as long as you need to do 20 without putting the bar down. The long and the short of the effect of this is it switches the body into grow or die mode because make no mistake about it – 20rep squats are TOUGH. If you can walk okay afterwards, you didn’t do them properly.

After your 20reps (only 1 set!!!) you go do some very light pullovers (like with 20 lbs) to stretch your ribcage out, and then you go through a very simple chest/back workout. Make no mistake about this, it may be simple and quick, but it’s almost as hard as your squats because after your squats you should literally have nothing left.

The milk part: You have to eat a LOT! It’s called Squats Milk because the bodybuilders of olde would down a gallon of whole milk per day on top of their usual caloric intake.

That’s the basic breakdown of it, but do the research and do not just go to the gym and do it based on this answer – I’m not giving you the whole thing. =P

Squats are just one weight training exercise out of many. To get bigger you will have to hit ALL major muscle groups using a balanced weight-training regimen, not just one exercise. Squats are primarily for your quads, though they will get other groups in your legs too, namely hamstrings and calves. If you’re interested in bulking up, I’d suggest you start putting together a training program with the help of a trainer.

You will also need to change your diet. Bodybuilders have specialized diets that are very high in protein and low in fat, but it is not always a very healthy option. I’d look into it or talk to a personal trainer, because trying to do it yourself can be unhealthy if you don’t know what you’re doing.

To summarize, squats are a good leg exercise, but that is it. You’ll need them, but you’ll need a whole lot more before you get results. Finally, squats are a great way of hurting yourself if you’re not careful, so I’d strongly recommend that you don’t rush into it.

The squat is performed by bending the legs at the knees and hips, lowering the torso between the legs, and then reversing direction to stand up straight again. The torso remains relatively upright throughout the movement. It acts as a supporting structure, unlike its role in the deadlift. Proper technique is critical, otherwise very serious injuries or gradual injury over a period of time can occur. The back must maintain its natural curvature and not round out (excessive lumbar or thoracic kyphosis), otherwise excess strain can be placed on the spine and cause serious injury. Lifting belts can be used to help support the lower back.

So yes, squats are a very useful excercise that can make a skinny guy (myself) turn into the hulk with hard work and proper nutrition.