This is a very simple question but something that I'm not able to wrap my head around. This Energy report states generated electricity. But what does "generated killowatthours" mean? I know that can't mean that the US produced that much electricity every hour...but what exactly does it mean?
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.