For knowledge to what it is electric power we should know what is electric current and the voltage. Electric current is the motion of electrons in large numbers. Electrons are very little particles that are in continuous motion in every material thing that we know. The voltage is the force that pushes those electrons in a desired direction.
Electric power is the motion of electrons with a determined force. This energy serves to run apparatuses that produce heat (light bulbs), light (or motion blender, vacuum-cleaner and (stove, plate) Motors in general).
Electric power is measured depending on the work that you do during a determined time. Your unit of measurement kilowatt-hours is kilowatt-hour. A kilowatt-hour is the work that is done (motion of a certain quantity of electrons with a determined force) during an hour.