How do I make a boxed extrusion on a cube that has a subdivision surface modifier? When I try to extrude a face on a cube that has a subdivision surface modifier it's always circular. Even when using edge loops. How can I achieve this? I'm new so I'm sure I'm missing something here. There is still a lot of things I don't know how to do. 

I would like to know how to get a box shaped extrusion (like the type of extrusion that you get on a cube with no subdivision surface on it) on a cube that has the subdivision surface modifier on it. The picture below shows what happens when I extrude on this cube that has the subdivision surface modifier on it. How can I make that circular extrusion rectangular?

Top picture is subdivision turned off and then you see in the bottom picture that when I turn it on my extrusion becomes circular.
Select the end face, and the four edges. Next press Shift+E to crease the selected edges.
You can also crease the edge loop at the base to make the extrusion like a cube. This method works mostly the same for extruding inwards as for extruding outwards. You may need to crease more edges, especially those on the face.