Hope this helps:
Directory Index
One of the more useful features of ".htaccess" files is the ability to change which default document you want to use. If the first page you want visitors to your site to see is titled "firstpage.pl", then you can instruct the Web server to display any pages named "firstpage.pl" before it returns anything else, when your site is accessed in the form of
http://www.mydomain.com. To do this, you'll use a "DirectoryIndex" directive like this:
DirectoryIndex firstpage.pl index.html index.htm
The filenames are listed in order of precedence. In other words, if no firstpage.pl, and index.html exist, the Web server will display index.htm as your default page.