Calories are a standard measure of energy. These calories estimate how much energy is needed to raise the temperature of 1 gram of water by 1 degree celcius. Calories supply the body with energy which is obviously essential to staying alive.
To burn calories, you have to use up more calories than you’ve consumed, this is called a calorie deficit. To efficiently do this, you have to calculate your TDEE, consume that amount of calories and either workout out more or consume less than your TDEE.
Total Daily Energy Expenditure is the estimation of how many calories you burn each day including physical activity. Please calculate your TDEE: link to TDEE calculator