A portion of the MDM Server documentation is available on the internet, however it doesn't include the sections which cover the MDM Workbench. The good news is that since the User Interface Generator was included with MDM Server for PIM, there is another information center which does cover the UIG part of the workbench.
There is very little difference between the versions of UIG supplied with MDM Server and MDM Server for PIM, so the documentation should apply to both. The minor differences in MDM Server for PIM are some extra data types (URL URL only, URL Image only and Nullable Boolean) and additional support for dynamic data.
So if you want to find out more about generating user interfaces, check out Introducing the User Interface Generator for all the details.