The control panel gives you the ability to modify the default documents for each of your sites,
so that you can configure which page or pages will come up when your site is accessed directly on its root
or a subdirectory when no filename is specified.

From your 'web options' screen for the domain you'd like to configure, scroll to the bottom and look for 'directory indexes'.
Turn that feature ON then enter the default documents (separated by a space) in the order you would like them searched.

For more information, please see the related link below.

http://www.drundo.info/doc/hsphere/html/manipulating_pages.html#directory_indexes