your burning calories all the time, beating your heart, using your lungs, digesting food, walking, typing on a keyboard etc etc.
The average calories used for a women is 2000 per day, and 2500 per day for men. So add 300 to this score to get a rough idea of how many calories your burning. It would be best to get a more accurate calculation on how many calories you use a day. Try but there's probably some better ones out there.