The application allows you to add the foods that you eat either manually, by searching for their names in the food database, or using the bar code reader. If you use the latter, you just have to scan the bar code with your device's camera and you will quickly have all of its information.
In addition to counting the calories that you ingest as food, Calorie Counter - MyFitnessPal also allows you to keep track of the calories that you consume when you exercise. For example, you can record that you ate a 500 calorie serving of pasta, but that you burned 200 calories running for a half hour.
Calorie Counter - MyFitnessPal is one of the best weight-loss applications out there. You can sync your progress with the official Calorie Counter website, which allows you to keep a consistent record of all the food you eat.