Aaron,
I quite don't get what you're saying but I'll explain how it works.
If you have a file called main.php, and in that main php you set a varialbe called $header = "This is the main page";
and then you include, from main.php, the file header.php (with require("header.php); or include("header.php")😉. In header.php you have a code similar to
<h1><?PHP print($header); ?></h1>
then you'll see the header text set in main.php
That's how I use it... and I know that many OO purists out there cry when they see stuff like that... but, hey, it works!
/Jocke