Weight loss is a simple equation. When you eat food you put calories into your body. Your body also burns calories to exist and when you exert yourself. If the amount of calories that go into your body is more than the amount of calories you burn, then these additional calories will be stored in your body as fat and you will gain weight. If the amount of calories that go into your body is less than the amount you brun daily, then the body will burn the fat stored in the body to make up for the shortfall.
The rate at which your body burns calories is called the metabolic rate. You can increase this by exercising and being active. So the idea is simple, increase your metabolic rate and reduce your calorie intake.
Your Basal Metabolic Rate is the amount of calories you burn in a day doing nothing.