You can take several approaches depending on how much time you want to spend.
First, you need to write down everything you eat or drink. Remember to include any supplements you take.
One approach would be to use the Nutrition Facts on the food label. Compare the serving size on the food label (which determines the calorie content) to the serving size you ate. Multiply the calorie value of the serving size on the Nutrition Facts label by how many servings that size that you ate. (For instance, say a 2 tablespoon serving of salad dressing has 80 calories and you typically use 4 tablespoons. Then you had 80 x 2 servings or 160 calories.) Write down that calorie value in a column next to the foods you ate. Repeat for each food you eat that day and add up the total. Now repeat this process for the next 7 days to get an average of the calories you eat each week including weekdays and weekends.
Since you eat differently on weekdays than on weekends, a weeklong analysis is more representative of what you eat on a usual basis. One problem with this approach is many simple foods like fruits, vegetables and meats do not have food labels with serving sizes and corresponding calorie values. Another problem is that more than 40% of meals are eaten outside the home in the U.S since 2014. The USDA has a new study of foods eaten away from home for 2017-2022 which results are not available yet. How would you enter calories/nutrients that don’t have food labels or nutritional information?
A second approach would be to give your food records to a Registered Dietitian who could do a nutrient analysis of your food intake over a week. They may even provide graphics that show what percent of the food you eat is fat, carbohydrate or protein.
A third approach would be for you to analyze your food records yourself with nutrition analysis software. It does require some time commitment to enter all the foods and beverages you eat throughout a week. Try My Food Record which I developed with my programmers to analyze the food you eat and it has 3 exercise tools to assist you in achieving a healthy weight.
The bottom line is if you eat more calories than you expend, you will gain weight. Research has proven that the people who lose weight and keep the weight off keep food records.