Working with Enhydra requires that you have a working knowledge of Java, and having some background in servlets will also help.
Enhydra is a relatively well-established product, but the documentation is taking some time to come into its own. In addition, a fair amount of the available documentation was written for Enhydra 2.x and 3.x and is thus somewhat out of date. I strongly suggest reading the Enhydra tutorial at
http://enterprise.enhydra.org/software/documentation/ee4b1/index.html.
An excellent article on Enhydra in general, with some examples of XMLC in action, was written by Roger Metcalf for the ArsDigita Systems Journal, http://www.arsdigita.com/asj/enhydra/.
Two complementary O'Reilly books provide enough information to get started with XMLC. Java and XML, written by Lutris employee Brett McLaughlin, describes the DOM in great detail, comparing it with SAX and other XML parsing possibilities. The second edition of Java Servlet Programming by Jason Hunter with William Crawford has an entire chapter on XMLC, following chapters on similar but competing systems for dynamic page generation using server-side Java.