For anyone browsing Links Beat, here is a clear starting point on the subject.
An electricity bill measures energy in kilowatt-hours, which is the energy used by a one-kilowatt appliance running for one hour. A two-kilowatt kettle running for three minutes uses a tenth of a kilowatt-hour, while a fridge running all day uses less power at any moment but adds up over time. Knowing this makes it easier to see where the money goes.