built.io supports notifications for iOS and Android. In Android, push notifications are provided by the GCM (Google Cloud Messaging) Service. To setup GCM, follow: http://developer.android.com/google/gcm/gs.html
To begin with this demo, you need a "Google API project" and an application on built.io.
Copy down your project number from Google API project and replace with "SENDER_ID" in "src\com\raweng\gcmdemo\MainActivity.java".
Replace your "Application UID" and "Application Api Key" from built.io with "API_UID" and "API_KEY" in "src\com\raweng\gcmdemo\MainApplication.java".