1-Create Firebase Account . 2- Make your first app in firebase dashboard 3- paste your link into Constants.java at FIREBASE_URL. 4-Run the app in your Mobile.
In this app you have a bad background,It is because of there is no drawable in this project but you can add your drawable , Initially i put mipmap/ic_launcher but you can give whatever image you want to be in background.
If someone is finding problem in login with google , go to sign up and then sign up, I will fix that bug very soon.
This app is created by the help of udacity resources .