It is just a tracking device. It doesn't really DO anything...
Whatever you consume, you record in the app. It keeps track of nutrient content, caloric intake and your goals... But you have to enter the information for it to work. If you forget to put in the crackers you nibbled, it isn't going to have accurate information in the data it uses to track your progress.
Many many many foods (including restaurants) are already in the data base that it accesses, so when entering your food it already has all the information, you just click the portion(s) size. But home cooked things take more work: you have to either add in the amounts of the individual ingredients in the items per the size of the portion of that item, or you have to do that separately and then include a "new" food which YOU input the data (calories, sodium content, fat grams, etc).
It is a tracking tool. No more, no less.
But does it help? Yes, if you are honest and keep up with entering your information throughout the day. That is how it helps--as you enter new information, you can SEE how many calories you HAVE consumed already, and how many you have "left" without eating too many in one day.
It also allows you to record your exercise, which increases the number of calories you can consume and still stick to your goals, and it has a preset amount of calories burned it uses for the various exercises.