kW is power
kWh is energy

If you use a 2kW appliance for 3 hours, you would've consumed 6kWh of energy.

Kilowatts is like the rate at which propane is flowing out of your tank.
Kilowatt-hours is like the total amount of propane you use in an hour.

Of course instead of propane, its electrical energy.

In heating language its called BTUs and BTU per hour. You buy natural gas on your heating bill in units of 100,000 BTUs, these are called a 'Therm'. The rate at which your furnace can heat your house is measured in BTU per hour.

Watts are like BTU per hour (rate of energy transfer)
Watt-hours are like BTU (total energy)

kW is a thousand watts (rate of energy transfer)
KWH is a thousand watts for one hour (total energy)

This is interesting because kW*h and km/h are sort of in an opposite situation in terms of which one is "rate of change" and which one is "total value".

• kW is a rate of change per unit time, it already includes the division by time in it (roughly kW = kJ/s)... e.g. something is consuming 10kW at this point.
  • kW*h is then the total amount of energy consumed over some time... e.g. over 5 hours we spent 50kWh.
• km/h is the rate of change per unit of time... e.g. you are driving 10km/h at this point (I'm using km/h instead of mph because that is more often used with the division symbol).
  • km is the total amount of distance between two points.
    • If you would want the the total distance traveled over time (similar to kW*h), then you have to multiple the speed by the amount of time traveled, e.g. (10 km/h)*5h = 50km.