Location: Settings link in Administration > Users > Authentication
With the "No Authentication" method enabled, a user can create an account without any kind of authentication from other systems, and with no email-based confirmation that the email address that they have provided is valid, or even exists!
This is a good way to create a very insecure Moodle site, and is not recommended.
This is an option that would normally be used only for testing purposes.
The configuration page for this option only offers the ability to lock fields, enable or disable guest access, and provide an alternative login page, in the same way as other authentication plugins.