Go to menu, under email+accounts, add your windows live account by selecting Outlook or Hotmail. Your first live account will act as the primary account for your Windows Phone.
if you have registered your windows account but it is still saying that you have not registered, consider updating your phone by downloading zune software
for a detailed tutorial pls visit http://www.freemake.com/blog/how-to-register-microsoft-account-id/
if you are an app developer and wants to develop apps for windows 8, you can get register and unlock your phone for app development with these tutorials http://michaelcrump.net/taking-a-look-at-registering-a-new-windows-phone-8-device-and-syncing-content