Not sure how to word that better or whether what is involved can be used with .html or only .php... but here goes. Say I have 100 pages - is there a way I can paste code into each of those pages and then control what is displayed on it from a single location? Like if I wanted to be able to change article links on the sidebar, etc., I would simply edit the single location and then have it reflected across all of the pages. I couldn't find anything on this, but as usual, I'm sure it's just because I don't know what it is called. And it probably requires .php but thanks in advance for any help.

Yes, I changed my pages to .php
The below was were my top navigation code was, I made a new file called topnav.php in a incl folder and pasted my navigation code in there.

If you put the below code on every page where the navigation menu is, then you can change every page by just editing the incl/topnav.php page
Saves a hell of a lot of time

<?php include_once ('incl/topnav.php'); ?>

Server Side Includes

Awesome - thank you both very much for the help!