Let us take an example: Say your goal is to lose weight, meaning you need to eat fewer calories than your body burns every day OR you need to burn additional Calories based on what you have eaten for both of these:
1. You need to know your Daily Energy Expenditure (TDEE) in Calories, based on your weight, gender, type of activity per day and your fat percentage.
2. You need to know your Daily Calorie Intake
3. You need to know your Daily Protein intake
4. You need to know how many Calories you burn daily, depending on your goal: either moderate and slow weight loss.
4. Having this information, we can now determine how many Calories you need to consume per day, to get to your target.
(Similarly if you want to gain muscle, and whether your goal is beginner or intermediate)