What they are saying is you have no pages (html, htm or php) in your root (primary) directory. If you do not have at least a index.html, default.html, index.php or index.htm in your root directory, it will display all your directorys like you see them now.
When you upload your PHP Nuke site, do not upload the site in the folder it came in. Upload only the files and directories contained within the distribution folder.
PHP-Nuke-7.4/html/
Read the install.txt file.