You start with an initial estimate of the number of calories per day your body burns. This doesn't have to be particularly accurate, since feedback will soon establish your own actual rate. Make an estimate using the tables on pages and based on your height, build, and sex. If you're active physically, use a number toward the high end of the range, and if your daily workout consists of changing channels, guess closer to the lower number. Don't worry about the exact number--it's nothing more than a guess.
If your goal is maintaining a constant weight, use the number directly from the table. If you wish to lose or gain weight, subtract or add the number of calories specified by your diet plan. (See page for details.)