Changing value in the include(" ") in PHP

Changing value in the include(" ") in PHP

Can anyone help me with this. I have a code in PHP that looks like this:
<?php
include("template/header.html");
include("template/navlinks.html");
include("template/index.html");
include("template/footer.html");
?>
This obviously holds HTML files showing them in a single webpage. My
problem is, perhaps a user clicks a link, how can I change the value in
the, for example include("template/index.html") to something like
include("template/about.html")
Somebody please help me out