Immediately after ordering The Recipe System you should receive an email that says Thanks for Purchasing The Recipe System.  This email will include your license key in the Product section below the product name.  Look for a 12 digit code comprised of numbers and letters.  This key will expire within a couple of days, so use it as soon as you can.  The key is tied to the email address that was used to purchase the system and that email address must be entered correctly to unlock the system.