I tried to find an animation of a correct squat, but none came up. This is a demonstration of how not to squat.
The problem being how far down he goes... you can see how his thighs never go parallel with the floor, this common mistake mistake is called "not going into the hole"A real squat should look more like this.
You can see how his thighs are parallel with the floor, this is the correct bottom position of the squat, it is important to keep your shoulders over the balls of your feet, or you will loose balance.