Widget Installation Problem

Sorry if this is a really stupid question but I cant get it figured out.

I have followed the following tutorial,
https://justintadlock.com/archives/2009/05/26/the-complete-guide-to-creating-widgets-in-wordpress-28
on creating a custom widget, and I have downloaded the example from the site so I’m assuming that there isnt a problem with the code.

The problem I am having is with actually installing the new widget. I have pasted the widget file in a few different folders to see if WordPress will auto detect it and display it in the admin widget panel, but this hasn’t worked.
Is there a place within WordPress that I have to include the new widget or should the register command in the widget file do that for me?

Thanks for any help.