installing php on apache

Hi, I'm a newbie to php having been working with coldfusion for years. Recently decided to test it out and have configured a box with Red Hat Linux 7.1, kde, apache and mysql. These all seem to be running fine but I can't seem to get a php page to translate. Im assuming that the web root is var/www/html and I've placed a file called index.php under that with a simple <php? echo ?> call. However it just displays the full file rather than translating the call. What am I doing wrong? All help appreciated. TIA Doug