The number of calories you should be taking in per day will vary depending on your stats (height and current weight) and activity level, and also how fast you want to lose weight. One pound is equal to 3500 calories, so to lose weight at a rate of one pound per week, you would need to take in 3500 less than you are burning per week or an average of 500 per day. Two pounds per week is a deficit of 1000 per day, etc. Taking the number from the Foods tab and subtracting it from the number in the Activities tab will let you know how much of a calorie deficit you have and you can adjust it. There is also a section under the Weight Goal tab entitled calorie restriction that calculates how much you should have as a deficit based on what you say is your goal weight and when you want to reach it.
An alternative that I prefer is to just use a calculator like this one: Calorie Calculator - Daily Caloric Needs