How do I enable the "Create new account" button on the login page?

To display the "Is this your first time here?" instruction and "create new account" button:

1. Make sure that the email-based self-registration plugin (or any other plugin that can support self-registration, such as LDAP) is enabled in Settings>Site administration > Plugins > Authentication > Manage authentication.
2. Select the self-registration plugin in the Common settings.