Hello,
I guess you are probably clicking to the link which is on our sample sites located above the page. Correct? This links point to the
CMS Desk and CMS Site Manager so that user is redirected there after successful login.
Therefore I would recommend you that you try to login using e.g. Logon Form webpart.
Then you can take advantage of the User contributions module in order to be able to manage documents from the Live site: http://devnet.kentico.com/docs/devguide/user_contributions_overview.htm.
Best regards
Ondrej Vasil