Please note that once you connect the game to Facebook, you won't be able to disconnect the game from it or use this Facebook account to connect another game to it.
You can connect your game to Facebook to save its progress. Facebook allows to synchronizing progress between both iOS and Android devices.
Connecting to Facebook
Open the game Settings and tap on the Facebook button:
Enter your login and passwords, then confirm them. Done!
Changing the Facebook account
Open the game Settings, tap on the Facebook button.
The game will reload and you will be able to connect to other Facebook account.