Just noticed this on the documentation index.
Apex now has an end users guide: http://docs.oracle.com/cd/E23903_01/doc/doc.41/e26811/toc.htm
I'm not yet certain it's a good idea linking users to this documentation in any user guides you create for your apps, given Oracle seems to like changing the structure of their links every couple of years, leaving documentation links that no longer work. Even so, it's worth knowing :-)
Current sections include: