Often it is undesirable to allow Joe Random visitor to sift through the files in directories like cgi-bin/ or graphics/. But sometimes it's nice to let people view the contents of a directory, for example on a publicly available file archive such as http://www.yoursite.com/files would probably want to provide a directory listing to visitors.
To do this simply add the following into a .htaccess file in your /files directory.

"Options Indexes"

To turn off directory listings add
"Options -Indexes"