After reading several articles on authorizing acces to a page on the site I have found none that explains how it works in the classifieds kit.  Can someone tell me where access to a particular page (postad.aspx for example) is controlled?  Mine works, I just don't understand why and I am in the process of adding another page that will require a user to log in first.

Access levels are controlled through web.config file for this site.  You can see access controlled via roles and login.