The amount of energy in an item of food or drink is measured in calories. When we eat and drink more calories than we use up, our bodies store the excess as body fat. Our bodies burn a certain number of calories per day, everyone is different and the number of calories you burn depends on many different factors. The main one being a person’s activity levels, the more active you are the more calories you will burn.
If your goal is to lose weight, then you want to consume less calories than what you expend. If you want to maintain bodyweight, then you should consume the same amount as what you expend. Then lastly, if you want to increase weight then you should consume more than what you expend. As you can see, the more important part would be figuring out your daily calorie expenditure. The easiest method for calculating TDEE (Total Daily Energy Expenditure) is to multiply your bodyweight in pounds by 14-16. If you’re a woman, smaller man, or less active, use the lower end of this range (14 or 15). If you’re a man, muscular woman, or very active, use the upper end of this range (15 to 16). There are much more accurate ways to calculate this, but this will give you a general idea.
Once you have figured out your daily calorie goal, you will need to achieve this consistently in order to start seeing results. A good way to make sure that you are sticking to your calorie goals would be to track your food and there are many apps that you can use to do this. You should see this as an educational process to give you an understanding of how much calories food and drink items contain. Eventually you will start to gain an understanding of what your body needs and how to control what you eat.