Find the meter. Some houses have one on the outside, while others have an interior meter. Make sure that you are close enough to the meter to accurately read the digital readout or the dials.
If the meter gives a digital readout, simply write down the numbers that are displayed. If the meter has dials, read the numbers from right to left, and record the numbers from right to left. When the arrow is between two numbers, record the smaller number. If the pointer seems to exactly target a number, record the number that is one below that number unless the dial to its right has a pointer that has passed zero.
Write down these numbers to give you the number of watt hours.