Something like hold finger up and close one eye then the other eye and finger moves? Is it the dominate eye that causes the finger to move?

Hold your thumb up at arms length. Look at something a good amount away like a tree or object that is easy to pick out. Look with both eyes and cover the object with your thumb. Then close one eye at a time but dont move your arm. The one that keeps the object covered is the dominant eye. This is important to know for sports and for recreational activities that involve aiming. The idea being if you are right handed and right eye dominant then you can find your aimpoint more easily with both eyes open. If you have opposing dominance then it will take more practice to shift for your aimpoint. (left eye dominant on right handed person).