At this moment, you could have already written an application manual following a template provided by GDP. However, you have not seen anything related with the final result, you only have seen a XML file with tags and texts. You will need to install some tools in order to can see the output of your tutorial, checking that everything is right.
The required packages for Debian users are:
docbookStandard SGML representation system for technical documents.
docbook-xslStylesheets for processing DocBook XML files to various output formats.
libxslt1.1XSLT processing library - runtime library.
yelpHelp browser for GNOME 2.
Optionally, you could install the next packages to generate the output in different formats:
xmltoXML-to-any converter.
dblatexProduces DVI, PostScript, PDF documents from DocBook sources.
For those who are not Debian users you can find more information at GNOME Handbook of Writing Software Documentation.
Firstly, you should check that your document is valid. You can use xmllint to do it:
xmllint --noout --noent --valid filename.xml
If it does not display any error then the document is valid. Otherwise you should modify your XML file to follow the DocBook reference.
Once you are sure that you have a proper document, you could see the final output using yelp:
yelp ghelp:/path/to/filename.xml
This program will open a GNOME help browser with your manual, you can navigate and see the different sections, checking that everything is right.
This will be the same result as when the manual will be integrated as application help.
On the other hand, you can generate different output formats from your document with different applications.
In order to get an HTML you could use xmlto:
xmlto html filename.xml or xmlto html-nochunks filename.xml
If you like to generate a PDF it is easier to use dblatex.
dblatex filename.xml
Moreover you could define your own stylesheet to generate a customized output.
Check the man pages of the different commands from this section, in order to know the possible options and arguments of each one.