I published a bunch of tutorials on my old blog, which can still be found at blog.zurka.us.
Feel free to check them out.
Adding this code to
LocalSettings.php will allow you to upload different filetypes to your wiki.
$wgFileExtensions = array_merge( $wgFileExtensions, array( 'pdf', 'ppt', 'doc', 'docx', 'xls', 'xlsx' ) );
To allow uploads you also need to change the owner of the folder to
# type in shell chown -R www-data /var/www/wiki/images/