The pool stance is the foundation of a good shooter and can be a difficult conept to describe since everyone's stance varies based on their body hieght/size for what is most comfortable to them. Even though most people do tend to have different stances, here we will cover the classic pool stance, which you can adjust depending on how comfortable you feel at the table.
The key to a good stance in pool is to make sure you line feet up with the shot before you get down on the cue ball. This means that you need to figure out where on the cue ball you are aiming and line up with this point by standing behind the cueball in the direction you will be shooting it in at the object ball. If you are a right handed player then you should have the center of your right foot directly on the line of the shot as you prepare to take your shot.
Your foot should be angled slightly outward when lining up in order to stay on the line of the shot effectively. Once you have your right foot in position take your left and step towards the table at an angle so that you feel comfortable on the shot.
Your feet width can vary depennding on your body type and the type of shot that you are taking on the table. Just make sure that you feel comfortable at the table and that your back right foot is lined up with the shot along with the rest of your body.