Kilowatt is the unit of power in the SI system. One watt is the power equivalent to one joule of energy being consumed in a second. Kilowatt is equal to 1000 watts.
Kilowatt hour on the other hand is a unit of energy. Power is energy divided by time; by multiplying power by time the resultant unit is again that of energy. As there are 3600 seconds in an hour, one kilowatt hour is equal to 1000*3600 = 3.6*10^6 J
If 500 kWh is consumed in one month, the amount of energy being consumed is equal to 1800*10^6 J.
Kilowatt hour is a unit of energy in International System according to http://www.ninjaunits.com/convert-joules-kwh/ Kilowatt-hour (kWh) can be converted to Joules and from here to another energy units.