I'm trying to create a php webpage. But everytime I try to preview it in my web browser (Firefox is the main one, but I tried in IE just to be sure) I only see the code. I'm using Apache 2.2 as a local server and it is installed correctly. Well, ok, I'm a novice with both programs but if I type in the browser http://localhost it says it works so I assume the server it's not the problem. I tried also with the Hello World code and it's the same story so it's not the code's fault either.
As editor I'm using NuSphere (that's what we use at university as well). Could someone please help me figure out what I'm doing wrong?

You haven't installed PHP on Apache so Apache cannot read php pages.
Try this tutorial:
http://www.php-mysql-tutorial.com/install-apache-php-mysql.php
If it does not work try working with XAMPP http://www.apachefriends.org/en/xampp.html