Signing in through game center, facebook or google play.
The basic way to sign in to an account is with a name and password. However you can also attach various other options depending on the platform you are playing on.
We allow facebook login from Android, iOS, Windows and Mac.
YOu can use Gamecenter for iOS
and Google Play on Andriod.
IN fact if you really want to make sure you have access to your account, you can attach any of these login methods to the same sign in name.
A problem that comes on on occasion, is that if the game doesn't have any knowledge of an existing account that was already signed in on that device, for example lets say you have an account you sign in to with on Windows, but you just got an iPhone and want to play there too. If you just sign in with Game Center, a NEW sign in name will be created which probably isn't want you want.
To connect a service like Game center to an existing account, 1st you'll need to use a sign in method that works across platforms (there is no game center on windows for example) . Facebook or Name and password work well. So on windows in this example, tap on your sign in name on the main menu of the game, and choose "account settings' and make sure you have an email and password set. then go to your iOS device, and use the "sign in" option and use that name and password to sign in with.
Now that your signed in to your iOS device, you can still attach your game center or other service, by going back to "account settings' and then on that screen, link the services you want to us.