More or less I agree with Connie.
There is only small trick to janickg reply: some Apache servers have this DirectoryIndex directive set by default as:
DirectoryIndex index.html index.htm index.php index.cgi ...
So if there is also in your case it means that the most important filename which server will look for is on the left side (if it didnt find this then server is looking for next going to right side).
So there is enough to put this the most on right file name to root dir of site and then server sends it as default page for site visitors leaving the rest of files as they are without need of doing next subdirs and so on.
Other thing is also that default setting is more optimal for server working but that isnt so important as you dont host to many sites on your machine.
This what janickg suggest to you is doing this default DirecotryIndex setting on own hand with own priority of documents. It is useful when server have other order of files then you want or then you can accept.
I belive that not it is a little more clear then it was few post ago.