Naturally, the best way to use UP by Jawbone's official app is in conjunction with one of its devices (on sale on their website). This will help you keep track of your physical activity throughout the day: steps taken, floors climbed, calories burned, and hours slept. However, the device is not strictly necessary.
Besides measuring physical activity, UP by Jawbone will help you keep track of your food and liquid intake. It will recommend how much water you should drink per day, and whenever you drink a glass you should input that in the app. You'll do the same with food, with UP by Jawbone giving you a daily calorie limit and letting you note down everything you eat.
UP by Jawbone is, in short, a great reference tool to develop healthy habits, since it will help you manage everything related to your health: your physical activity, dietary habits, water intake, etc.
Requires Android 4.3 or higher