I thought I did this yesterday but my mate edwin said it was never posted, so don't blame, they never found it, im not duplicating posts. Heres again, enjoy.
The main advantage of using DocBook is its multi source nature. This means only one DocBook source file is needed to make many different outputs. From the same DocBook file the user view the documentation as HTML and can provide a print copy, usually in PDF. Docbook facilitates the user many different output formats from a single source file. These are some useful resources to get you started:
http://www.docbook.org Norman Walsh's DocBook: The Definitive Guide. Online O'Reilly book on using DocBook. Contains an excellent element reference. May be too formal for a beginner.
A Practical Introduction to DocBook (http://www.ibiblio.org/oswg/oswg-nightly/oswg/en_US.ISO_8859-1/articles/DocBook-Intro/docbook-intro/) The Open Source Writers Group's introduction to using DocBook. This is an excellent HOW-TO type article on getting started.
Getting Going with DocBook: Notes for Hackers (http://nis-www.lanl.gov/~rosalia/mydocs/docbook-intro/docbook-intro.html) Mark Galassi's introduction to DocBook for hackers. This has to be one of the first introductions to DocBook ever - still as good as it ever was.
Dave Pawson's DocBook FAQ (http://dpawson.co.uk/docbook/) Dave Pawson's FAQ on everything DocBook related. He discusses references, tools, catalogs, and stylesheets in a concise FAQ format. One of the best resources to find answers to common questions and problems about DocBook.
FreeBSD Documentation Project Primer for New Contributors (http://www.freebsd.org/doc/en_US.ISO8859-1/books/fdp-primer/index.html) FreeBSD documentation project primer. Chapter 4.2 provides a very good introduction to writing documentation using DocBook. Note that it also describes some custom extensions of DocBook; fortunately, they are clearly marked as such.
You you get in your way better resources feel free to add them here or even feel free to give feedback on which you found more useful.