A calorie is a measurement unit of energy.
These are listed on food items, which are an estimate of the total energy that your body will derive from that food item on consumption.
The Calories mentioned on food labels are usually expressed in kilo Calories (Kcal). So next time when you shop doesn't forget to check the food label for nutritional values.
Try to go for those products which have more amount of protein and some vitamins or minerals.