If you reset your device, or must re-install for some reason, your progress MUST be associated with an account or YOU MAY LOSE PROGRESS BY UNINSTALLING
You can connect your game with your Facebook account Apple account, or create an account using your email address.
To connect via Facebook, go to the Settings Screen (gear icon)
and under "Back Up Your Account" choose either Facebook or Email, and fill in the information.
That way If you have to re-install, you'll be able to sign in using that information.
Note: If you have done a fresh install, you'll have to go through the first couple of tutorials to get to the main screen with the gear icon.