You can save your game by connecting it to a Google Play account.

Google Play supports only one save game per account and trying to use multiple games with one account may result in the loss of your save(s).
  1. Open the Google Play Games app on your device
  2. Log in with your Google Play account
  3. Launch the game and open the Settings in the upper left corner of the screen
  4. Tap “Connect to Google Play” and your game status changes to “Game Saved”