Basic newbie question regarding navigation links

[eluser]sehummel[/eluser]
I'm brand new to CI and have a very basic question. As I recall from my previous limited experience with CI, to refer to a controller in the navigation, we put <a href="controller_name"> rather than adding the PHP extension to it. But yet I get a 404 error when I do this. I know my second controller works because I can load it as the default controller and it loads my view.

What am I doing wrong? The controller is in my root controllers folder