UKCIG - http://www.ukcig.info/ is the HTML website . I want to convert in PHP.

Technically, all you need to do is to change the file extension from .html to .php, and update your links. A proper PHP programmer e.g. me can take it up from there to make it very dynamic and utilize PHP functionalities.

Just as dhtml18 said, just change the extensions of your files from ".html" to ".php"
for example index.html should be changed to index.php

Secondly, any where in your file you want to use PHP functionality just put the opening and the closing tags of PHP
<?php Your PHP Script here... ?>

Na so