First off, you will need a valid Square Enix account in order to use the PlayOnline service. Once you have acquired a Square Enix account, log into the Square Enix Account Management System, and create a service account using the registration code.

There is a dedicated page set up specifically for new customers and returning customers, so please review which procedures apply to your situation and complete them accordingly.

<Square Enix Account Transfer Page>
http://www.playonline.com/homeus/polshift/