Is your Apache configuration aware of PHP? Create a file with the contents below and call it info.php:
Put it in a web accessible directory (in the Apache document root, perhaps?) and access it through your browser. If PHP is setup correctly you will find a long page with information about the PHP environment and related settings.
If it doesn't render the page I suggest you browse the PHP manual which includes very verbous installation information - what needs to be in your httpd.conf and so on.