How do I get the Classic Wii controller to work?

I just tried to use my classic wii controller that I ordered, and it isn't working. All I have to do is plug it in to the wii remote right? If that is wrong then please tell me the correct way to do it.I am trying to use it with a gamecube game.So if I can't use the classic wii controller for gamecube games I guess ill just return it and get an actual gamecube controller, it would be way better if they made a wireless gamecube controller.