Erica,
It depends on how you are installing WordPress...
If you are manually installing then you would want to install it in the /www Directory.
However if you are using the App Manager then you would want to leave the directory name blank so that it installs as noted below
"The domain and directory selected above represent the URL (web page link) shown here:"
http://mydomain.com/
The installer will automatically install it in the /www. If you add www as a Directory it will end up being installed as
http://mydomain.com/www which is not what you want...
-Bob