Gradle instructions
Alternatives:
Unity
C++
The Google services plugin for Gradle loads the google-services.json file that you just downloaded. Modify your build.gradle files to use the plugin.

Project-level build.gradle (<project>/build.gradle):

buildscript {
  dependencies {
    // Add this line
    classpath 'com.google.gms:google-services:3.2.0'
  }
}
App-level build.gradle (<project>/<app-module>/build.gradle):

dependencies {
  // Add this line
  compile 'com.google.firebase:firebase-core:11.8.0'
}
...
// Add to the bottom of the file
apply plugin: 'com.google.gms.google-services'
includes Analytics by default help_outline

Finally, press "Sync now" in the bar that appears in the IDE: