yep.
1) the fastest way to start getting use out of php is to rename the files to .php or .php3 (depending on your system setup).
2) create a nav bar in html (just the table to create the nav bar, nothing else) and name the file something like nav.php.
3) in your web pages, add the nav bar like so:
<?
include("nav.php");
?>
when the page loads, php will insert the contents of nav.php into the web pages.
you might want to place the nav bar file into a folder that just has common page elements.