You can speack about potential energy (Ep) when you have tow masses, for example the mass of Earth and a bowling ball. lets note the masses :Earth has mass noted with "M"and the mass of the ball is note with "m". If the distance between ball and Earth is d = 10 meters, we can say that the ball is in the potential field of Earth because the tow objects interact eachother with gravitationa forces. So at d = 10 meters we can dfine the potential in that point and we called the potential energy (Ep) and the formula of it is Ep = mgd ... m and d we already define and g= grvitational accleration. I choose thise example and explain it that way because is a easy one and M >> m.
