To lose weight, you need to be at a calorie deficit. That means consume fewer calories than you burn each day. It's math; if I'm taking a math class, I'd like to have a calculator with me if I'm allowed to, rather than just "guess"!
MyFoodDiary also breaks down your calorie consumption by fat, carbohydrate and protein percentages, which is REALLY important when working out to gain muscle and lose fat. There are features that make food and exercise tracking easier than other apps I've tried, you get a free week trial and then it's less than $10 a month. Yes, there are free apps out there. But you get what you pay for, and I think this is worth every penny.
I'll be holding a free seminar to show the cool features of this app, and will post the dates soon! Hope you can make it!