Development > Membership, permissions and security > User registration:
There are three different ways how you can let site visitors register on your site:
•Using the Registration form web part. Read more here.
•Using the Custom registration form web part. Read more here.
•Via Third‑party authentication. Learn more here.
Help URL: http://devnet.kentico.com/docs/6_0/devguide/index.html?available_registration_web_parts.htm