We will first define a few achievements in the developer console and then see how to unlock them in the game. Note that to publish any game with GPGS, you need to define at least five achievements. No other feature is mandatory, but achievements are.
We need to define at least five achievements to publish a game with Google Play Game services.
If you want to use GPGS with a game that has no achievements, I recommend you to add five dummy secret achievements and let them be.
To add an achievement, we just need to navigate to the Achievements tab on the left and click on Add achievement:
The menu to add a new achievement has a few fields ...