To convert to man pages, you run the command docbook2man (see Wrapper scripts manual page). For example,
$ docbook2man --solinks manpages.xml
The man pages will be output to your current directory.
The --solinks options tells docbook2man to create man page
links. You may want to omit this option when developing documentation
so that your working directory does not explode with many stub man pages.
(If you don't know what this means, you can read about it in detail in db2x_manxml,
or just ignore the previous two sentences and always specify this option.)
To convert to Texinfo, you run the command docbook2texi (see Wrapper scripts manual page). For example,
$ docbook2texi tdg.xml
One (or more) Texinfo files will be output to your current directory.
The rest of this manual describes in detail all the other options and how to customize docbook2X's output.