You have to make sure  you have AllowOverride in your httpd.conf for mod_rewrite to work.

To make the rewrite active for a website you have to change the .htaccess file

An example of the content would be:

Options +Indexes
Options +FollowSymlinks
RewriteEngine on
#RewriteBase /
RewriteRule ^(.*)\.html$ $1.php [L] 

This script converts all requests to a .html file to a .php file. So it appears as a HTML file to the end user.

To test if PHP is setup correctly on your web server, or to check your PHP Configuration.

You just need to add the below code to your a .php file:

<?php phpinfo(); ?>