If you are an overweight or obese adult, you probably eat too much i.e. more than you actually need. As a matter of fact, your body needs a certain amount of calories to keep itself functional and active, and if you eat or drink more than that, you will likely gain weight. Likewise, if you consume fewer calories than you expend, you will lose weight.

How many calories do you need? Well, that depends on a lot of things. Your age, sex, type of work, physical activity, all come into play. There is no one answer for this type of thing. I have to warn you, I don't believe the general ideas on how many calories a person should have.