Gui Essentials Collision Tutorial didn't work

Hi I am new to unity, and I was following the gui essentials tutorial to get started. At the end it had me create a plane and two boxes the bottom box has a box collider and the top box has a rigidbody, which has gravity turned on. The tutorial says that when I play the scene the top box will collide with the bottom box, and land on the plane. However what happens is the top box goes right through both the bottom box and the plane. I have search the forums and tried changing many of the different options and can not figure this out. I'm sure this is something simple I am missing, any help would be appreciated.

Add a box collider or mesh collider to the plane. Make sure there is also a box collider or mesh collider on the bottom box