Google
You can connect your game to Google from the game settings. Tap on the cogwheel at the top right of the screen, and then tap the Connect button. After that, tap the button with the text "Google Play Games." Your account will now be connected.

Once you have connected your game to your Google account, your game progress will be saved to that account. If you ever need to reinstall the game or wish to play on another Android device, you can restore your progress by connecting to the same account.

If you manually disconnect your game from your Google account, your progress will no longer be saved, and you will be unable to recover it if you reinstall the game.

Facebook
 You can connect your game to your Facebook account from the game settings. Please tap on the cogwheel at the top right of the screen, and then tap the Connect button with the Facebook icon on it. You will then be prompted to log in to your Facebook account.