Get the project
If this is your first time using a Google services sample, check out the google-services repository.
$ git clone https://github.com/googlesamples/google-services.git
Open Android Studio.
Select File > Open, browse to where you cloned the google-services repository, and open google-services/android/gcm (if you are in the Android Studio start screen, you can select Import Non-Android Studio project and use this same path).