Assuming you're not dead, your body burns calories 24/7/365. Do you know how many calories you burn just sitting on your butt all day? How about if you're active? Knowing your caloric burn each day can help you plan your diet to reach your fat-reduction goals.
Check out Alice's blog, where she's posted information that will help you calculate your base metabolic rate (BMR) - the rate at which you burn calories while just sitting around breathing.
Be well!