Fitbit is an app that lets you keep a complete record of your physical activity as well as your eating habits and even your sleep schedule.
The optimal way to use the Fitbit app is alongside one its devices (for sale on its webpage), which help you measure your physical activity throughout the day: the steps you take, stairs you climb, calories you burn, etc.
Besides measuring your physical activity, Fitbit also helps you keep a record of the water you drink and the food you eat. The app recommends a daily amount of water you should consume, so each time you have a glass you should note it down on the app. Fitbit also recommends a certain number of calories you shouldn't go over in a day, and lets you write down the food you eat.
Fitbit, in short, can become a central switchboard for keeping your habits healthy. It lets you control everything about your health: athletic activity, eating habits, water consumption, etc.
