This website uses Launchpad for user authentication.
If you don't have an account there, you will be invited to create one on your first login here.
If you registered on this site before the installation of the Launchpad integration, you will have to log in manually and add the https://login.launchpad.net OpenID identities to your account.
Ask the below support points for a free Ubuntu installation set. Many of us will also happily offer you an Ubuntu demonstration or help you the first time you install Ubuntu.