We assume that you are installing/playing around with WordPress 1.5.1, in that case please have the following code in your index.php file.
To start, use a program like “wordpad” on your machine and enter the text below into it. Save it as index.php in a location you can remember, now open your FTP program and connect to our website. Then from the location on your local computer where you saved the index.php, copy it over to your website.
The code is:
<?php
/* Short and sweet */
define('WP_USE_THEMES', true);
require('./wp-blog-header.php');
?>
This is necessary to get your website working.
Secondly, .php != .html. Let me explain.
When you create a website and visit it with a browser, your browser talks to the web server and has to start feeding your browser some file. By default, under Apache (a free Unix/Linux web browser) this file is usually index.html (index.htm sometimes).
This could be considered the FRONT DOOR to your website, from there you can use HTML code to direct visitors to other files and so on.
Now let’s move to the PHP age of dynamic web creation. Here your FRONT DOOR takes on a slightly different aura in the form of index.php. Apache now has to instructed to look for this new file to get you going. WordPress is a PHP program that uses the index.php file to get started.
Without a valid index.php, your website will be like a house with no front door.
Other web servers and sever-side scripting languages (PHP is one of these) use different index.<extention> file. You can have index.asp, index.jsp, index.php, index.cfm, and of course the venerable index.html/htm.
Phew..:) hoopefully that wasn’t too much information..
Regards