Change default dir page
Most hosts will specify that your default starting page should be named index with whatever extension on it (usually .html). Using the abilities of htaccess, you may change this behavior to specify any other page and extension you prefer.
You may also list an assortment of filenames in case you have different directories and want to load in the appropriate default page. Give the command a list of values. The command will go through the list one by one and will display the first valid one it comes across.
When a visitor tries to access the directory this htaccess is contained in, it will try to find filename.html to display it. If it isn't found, the next entry is tried, and so forth down the line...
What if none of the files exist?
The visitor will be shown the 404 Page Not Found error page.