Create a basic index.php file
From Joomla! Documentation
The index.php file becomes the core of every page that Joomla! delivers. Essentially, you make a page (like any html page) but place php code where the content of your site should go.
For many reasons (such as: bandwidth, accessibility, and W3C standards compliance) you will want to make the index.php file as small as possible and use a separate css file for styling. This example will show how to create a simple layout using the <div> tag.
Lets start at the top:
<?php defined( '_JEXEC' ) or die( 'Restricted access' );?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="<?php echo $this->language; ?>" lang="<?php echo $this->language; ?>" >
The first line stops naughty people looking at your coding and getting up to bad things. The second tells the browser (and webbots) what sort of page it is. The third line says what language the site is in.
Now the header for real:
<head> <jdoc:include type="head" /> <link rel="stylesheet" href="<?php echo $this->baseurl; ?>/templates/mynewtemplate/css/css.css" type="text/css" /> </head>
The first line gets Joomla to put the correct header information in. The second creates a link to your style sheet. You will need to change this to the directory name that you chose.
Now for the main body: