The farther apart your feet are, the more it will restrict your lower body from turning, while the closer your feet are, the more it will promote your lower-body rotation. If your stance is too wide, you'll slide or sway through your swing and hit erratic shots. There should be about one hand span between the grip end of the golf club and your belt buckle. The farther away you stand, the more you will be inclined to swing the club around your body. The closer you stand, the more inclined you will be to swing the club away from your body.
Correct posture is one of the keys to a sound golf swing.
Your legs should be relatively straight with a slight flexing of the knees. By bending your knees, you stop your lower body from rotation, which will cost you both in terms of distance and accuracy. Most of your weight should be on the balls of your feet or under the bottom shoelace. Your upper body should lean slightly forward with your bottom sticking out. Make sure your upper body is bent forward about 30 degrees.