dwr has given you great information, and all that is correct. The only thing that I would add is this:
It's a little unclear from your post what you are seeing when you say "the website still shows the index".
1) If the "index" you are seeing contains a list of numerous files, then the problem of an index showing instead of a "site" can be attributed to the fact that you do not have a file named one of the file names the DH Apache server instance recognizes as a, as you say, "mainpage". This can be corrected as dwr described.
2) If, however, the "index" that is showing is "empty", then you have uploaded your files to the wrong directory.
Hopefully that will be of some help; if not, post back with some additional detail (maybe even a url to your site), and we will try to help further.