If you do not have one, make one. A cone.
Get a piece of cardboard, or printer paper if you don't have cardboard, and make a cone.
Place your cone on a flat surface and put a light source on one side of it. If you don't have a table lamp, use a torch. Now draw the cone with shading. I want to see 5 values please.
Get a cardboard box, big enough to put your cone in.
Cut he top off, and the front off. Cut a hole in the side. Place your cone inside the box, and your light source outside the hole. Now you have some pretty neat shading and shadows..
Have fun. :-)))