Server Side Includes with .shtml
Here is a brief example of a server side include and an some links to more in depth explanations.
The Basics for Server Side Includes
First, cut all of the pieces of your site that are used on more than one page and paste them into separate files in a folder called "includes". Change the file extension for your main pages from .html to .shtml.
To link to the include you would insert a line of code that looks like this:
- <!--#include virtual="/gordon/template/includes/navigation.html" -->
Server side includes will not work if you try to preview your site on your computer. You need to upload your file to the server for it to work. Hence, server side includes.