From Bayohne:
The pre-order codes that are being distributed for North America and Europe include instructions that they will be redeemed via a special website:
NA: http://preorder.na.finalfantasyxiv.com
EU: http://preorder.eu.finalfantasyxiv.com
This special site is not yet live for users to redeem the codes received from their retailer.
Once the code redemption for this site is live, scheduled for August 20, 2013, you will be able to enter the code you received that looks like: ABCDEF-###-ABCDEF-###
That will then give you all the instructions required to register your early access code. 
In short, hang tight guys and don’t panic!
the interblag 