Your game should be linked to your Facebook account. To do it open Settings and bush the Connect with Facebook button. If you do this from another device (we mean - connect your account with the same Facebook account), you will be able to continue your game from where you left off.
Also on Android you can additionally link your game to Google+, on iOS - to GameCenter and on Amazon Kindle - to GameCircle.
If you have some problems with it, please, let us know by using Support button in the Settings or via firstname.lastname@example.org