When you install from CD, you are installing in trial mode and can use it for 15 days before subscribing/activating the subscription. Open OneCare and click on the link within OneCare to subscribe. Sign in with a LiveID (http://account.live.com or the one you used to sign in here) and then select the option to subscribe with a retail product key or PIN, which you will find inside the package, behind the disc tray on a yellow/orange sticker. That will start your subscription and OneCare will receive the activation credentials and will show you current subscribed status and the expiration date of 12 months from activation.
-steve