Simple theory: burn more calories than you put in
Harder to put into practice though. The best way to burn your calories, however, is through muscular exercise. And believe it or not, the "stronger" your muscles become, the more calories they require to live. So basically, if you exercise your muscles, not only will you burn more calories than any other process, you will also burn calories when you are simply sitting down. Great huh. So, the sooner you start that, the sooner you will start to burn calories when you asking questions on yahoo answers. This is all called your metabolism.
So what is muscular exercise?
Basically, its any kind of exercise you will feel pain in. But don't be discouraged by pain because you will feel great afterwards. And don't worry, you eventually become mentally strong enough to push through the pain. Try doing some push ups, sit ups and squats. Don't worry about becoming "to muscly" or something like that, because I guarantee you it takes years and years and years of very hard and vigorous training to reach that level. Basically, you want to be aiming for a nice, toned body - The best type of body you can get