On the login page go to "Don't have an account yet?" and then to "Create a POK account (no certificates)". Once submitted the form, you will receive an e-mail with a link to activate your account.

If you do not receive the activation e-mail within a few minutes, try to check that it is not in your junk mail folder.

If it is in your junk mail, mark it as mail to be delivered to your main mailbox. Don't forget to open the link to activate your account.