Google Fit is Google's official app to help improve your health
in a very simple way: by telling you how much exercise to do each day. Users have to set themselves some daily and weekly goals; these can be anything from a 45-minute run in the afternoon to a 10-minute bike ride on the way to work. Whatever the activity, it will be added to your activity chart.
You also have to enter your weight and height to start using Google Fit, because that's how you'll know if you're losing weight. Of course, even if you enter all your workout plans into Google Fit, if you don't actually do them, the app will alert you and see your absence reflected in the chart. So you'll have an extra incentive to work out.
Google Fit is a very useful app and like almost all other apps developed by Google, can also be connected to your Android Wear device and can even be consulted on its official website.