You can find the official PHP-Nuke documentation at:

http://phpnuke.org/modules.php?name=PHP-Nuke_HOWTO
http://phpnuke.org/modules.php?name=FAQ

In addition, you may have a look in our resources by logging into your Customer Area -> Get Support -> Get Support - HelpDesk (at the left side of your screen) -> Other Resources (at the bottom of the displayed page).