...
In order for a PHP file to be callable via main.php it has to have a record in the files table files. This requires a relation to an area in the area table area. An area can best be described as a set of backend scripts that serve a common purpose and belong to a subnavigation item. It's not much more than a name having some properties which will be described in the area page in detail. As you might have seen the CONTENIDO backend still uses frames. In order to let CONTENIDO know in which frame a script will be displayed in, the record in the files table files has to be mapped to its frame which is achieved by another record in table frame_files table. With all these records CONTENIDO is able to call a script, but still a link, i.e. a navigation item, to call it is missing. That's what the main- and subnavigation is needed for.