Let’s start by defining a kilowatt hour. Different devices have different wattages: The average microwave, for example, is between 600 and 1,200 watts. To simplify things, let’s say you own a 1,000 watt microwave. If you cook your frozen meals for 5 minutes, and you eat 12 frozen meals a month, then you’ve used your microwave for an hour in total (you should also probably cut down on frozen meals).
Since your microwave is 1,000 watts, and you’ve used it for one hour, you’ve used 1 kilowatt hour for that month (just multiply the wattage by the number of hours used, then divide by 1000).
Here’s another example: If you run a 1,400-watt window AC unit for 8 hours a day, every day of the month, that will use up about 336 kWh for the month. Here’s the math: You used it for a total of 240 hours that month, because 8 hours a day x 30 days = 240. So, multiply the wattage (1,400) by the number of hours used (240), and then divide that by 1,000. Voila! Your AC unit cost you 336 kWh.