SSI- Server Sides Included
SSI is simply a different way of using php. Once SSI is added up, all you have to do to change the sidebars is edit one page, and it's automatically edited on all pages. It's very simple but with the wrong explanation it can be very difficult, so here are my simple intructions for those of you who get lost easily like me:
First, make a page called left.html (or whatever you choose to end it, like .htm or .shtml). Add whatever you want in the left sidebar of your website on that page.
Next, make a page called right.html (or again, whatever you choose to end it). Add everything for the right toc and whatever ends your layout html. If that somehow confuses you then just put everything you want to see on the right in this page. ^^;
On all other pages that will display contents in the middle, including your Main page, follow these instructions:
On the very top of every page, add this code: <*!--#include virtual="left.html"--*>
Take out the stars but nothing else! If your page didn't end with .html, change that to whatever you ended it with.
On the very bottom of every page, add this code: <*!--#include virtual="right.html"--*> Take out the stars but nothing else! If your page didn't end with .html, change that to whatever you ended it with.

And that should be it. When you view the pages, the two codes should turn into the left and right pages you made.

Having Problems?
1. Make SURE the left code is at the very top and the right code is at the very bottom.
2. The left and right codes should not be on the left and right pages. In other words, left.html should NOT have the code <*!--#include virtual="left.html"--*> (without the stars) anywhere in it.
3. Make sure the files for everything are named correctly.
4. If something still comes out wrong, put all your html in one file and seperate it into three parts, the left, middle, and right. After seperating, try re-doing the SSI.