The Registration form web part is a ready-made web part that can be used right out of the box. You can just place it to any page of your web site without setting any web part properties. However, if you want to modify the default behavior of the web part, you can set a number of web part properties. You can find a detailed description of these properties in Kentico CMS WebParts reference guide.
Page url: http://devnet.kentico.com/docs/devguide/index.html?registration_form_web_part.htm