The whole purpose of using Joomla and K2, is to build websites that are easily editable by the user. However, this does not mean that the whole website is editable by the user. This blog entry highlights what functions should be left to the developer/designer, and what functions can be edited by the user.
User fields allow you to add users and edit their permissions so they can access and edit your website. Learn how to edit user fields in Joomla and K2.