To login properly using Words with Friends App, please check these steps:
1. After you launch the app, there's an option to load your game using Facebook if you already linked the game to your Facebook account.
2. If you are not connected to Facebook, you can create an account using email (Sign up with Email) or if you already have an existing account, tap the Log in now to load your game using the Email you used to create your account.
Note: Please make sure that you enter a correct email address to avoid creating a new account.