Using this Google Play Services asset, you can implement a wide range of Google services in one go:
If you do not require IAPs or Google Play Licensing support in your game, simply don't select those extensions when importing this asset (or you can just delete the extensions out of your project afterwards if you Import All).
1) To be able to build a project with the Google Play Services Extension, you'll need to install the Google Repository: Android Studio > SDK Manager > Android SDK > SDK Tools > Support Repository > Google Repository
2) For logging into Google Play, make sure that you're targeting your own Google Services ID in Game Options > Android > Social. You may also need to upload an APK to Google Play Console before you'll be able to log in to Google Play on your app. When signing into your game via Google Play Services, you must be using an executable that has been signed in the project with the same keystore as the one initially provided to the Google Play Console, otherwise login attempts will be rejected and will return -1.
3) To test Achievements and Leaderboards, you'll need to create your own game on the Google Play Console and create achievements and leaderboards for it.
4) To test IAPs, you'll need to create your own game on the Google Play Console and create the IAP products for your game on the web panel, then ensure your Google Licensing Public Key is set in Game Options > Android > Packaging, implement your initial IAP code, and then also upload an .apk to Google.
5) To test licensing, you'll need to create your own game on the Google Play Console and enable the use of Google Licensing, then ensure your Google Licensing Public Key is set in Game Options > Android > Packaging (same values you may have already done for IAPs), and then also upload an .apk to Google.