The key to learning the mat room is to just take a day and PLAY with it. don't look at it as work or trying to accomplis something. Just load up a fairly simple object... like say a chair or a table and start plugging nodes. Use the eyedropper tool to select a material (I LOVE the eyedropper) then just go thru the list of materials that come with P5... pick one... change the mat (by double clicking in the library) then Look at the structure of the mat.,.. Thats a good way to learn how a shader is put together. Most important thing is don't look at it as a daunting task, that you are afraid to fail at. Just look at it as a new toy or game to explore and play with. You can't screw anything up. (unless you save it. :p)