In the Settings | Authentication screen, Local Database is the default value you start out with
This option uses the help desk database to manage and authenticate your users. The other option is SAML authentication.
When this option is set the login screen for the help desk will have a "Forgot password" link, allowing users to send a password reset link to their email. This option is not available with SAML authentication.
Also, you have the option to turn on "Allow users to self-register"
This will show a "register" link on the login screen. Allowing anyone to create their own account.