I\'m unlocking achievement using this simple method from developers docs:
Games.Achievements.unlock(getApiClient(), \"my_achievement_id\");
Just add a view to the layouts you want to display achievements on like this:
When you have your layout ready you neet to execute this inside your Activity or Fragment:
Games.setViewForPopups(getApiClient(), findViewById(R.id.gps_popup));
You have to be sure, that your GoogleApiClient is connected though, otherwise your app will crash.