A calorie is a unit of heat that used to measure how fattening foods are. You always want to choose foods that are lower calories.
It takes about 3500 calories to make up a pound of weight. If you get your calculator out and divide 3500 by 7 day you get 500 calories. So you goal is to lose 500 calories or 1/7th of a pound each day.
If you eating poorly, then reducing your calories shouldn't be that difficult.
Drink water vs. regular soda - 150 saved per can. Three cans and you're down 450 calories
Eat lower calorie items at restaurants. Some meals are 2000 calories and some are 500. Choose wisely.