What are calories? why are they needed?

A calorie is a unit of energy. In nutrition, calories refer to the energy people get from the food and drink they consume, and the energy they use in physical activity. Calories are listed in the nutritional information on all food packaging. Many weight loss programs center around reducing the intake of calories.

Explanation:

i can't answer your question in very sad situation.

but if your situation is very bad, then you can find happiness by thinking about your past that has full of happiness.

or you should do meditation for some time to get rid off from that bad situation.