Kilowatt Hour Definition
You are confusing kilowatt hours with kilowatts per hour (which is a fairly useless measure of anything).

A kilowatt is a measure of the rate at which energy is delivered (also known as power). One kilowatt means that 1000 joules of energy is being delivered every second.

A kilowatt hour is a measure of total energy delivered.

kilowatt      = energy/time

kilowatt hour = kilowatt x time
              = (energy/time) x time
              = energy


So if your water heater draws 6 kilowatts when it is on, and is on for 30 minutes, then it has consumed 3 kilowatt hours.

According to the report:


  In 2011, the United States generated about 4,106 billion kilowatthours of electricity.  About 68% of the electricity generated was from fossil fuel (coal, natural gas, and petroleum), with 42% attributed from coal.


kilowatt hours = 4,106,000,000,000 kWh

hours          = 356.25 days * 24 hours/day
               = 8766 hours

kilowatts      = (kilowatt hours) / hours
               = 4,106,000,000,000 kWh / 8766 hours
               = 468,400,639 kW


So we can see that during 2011, if you were to measure the power being generated in the USA, it would be about half a Terawatt.