AM server by itself has Security Console, Operations Console, and Self Service Console.
A WebTier is an installer that will install on RedHat or Windows and it mirrors the functions of the Self Service Console, and can be placed anywhere (usually placed on the DMZ so it can be accessed over the internet for users to do CTKIP or Self Service Operations w/o needing to be VPN into internal network). So, it is essentially just another Self Service Console that prevents you from needing to make the actual Self Service Console exposed to 'the world'. Like a proxy, you can expose the WebTier and not need direct AM server Self Service Console exposure. If you use a WebTier, both it's Self Service and the real Self Service pages continue to work (it doesn't shut off the real Self Service Page internally).
