Embed content into a page. With this you can update one page (ex. navigation) and the code will update it on every page.
PHP Includes allows you to embed content into a page. This is very similar to SSI, since it allows you to modify one page to update many. This will save you a lot of time if you have a large site. Your host must support php. This works for any file except .shtml pages.
<?php include("path or url to file"); ?>