@Guzel,
Power is energy divided by time. "mgh" is the standard potential energy formula (how much energy is required to raise a mass of "m" a height of "h" in a gravitational force of "g"), but there are other ways to compute energy. For example if you accelerate an object from a standstill to a velocity of "v" with no change in elevation, then energy is 1/2 mv^2 (kinetic energy).