how to add shape to the top of a piece of wood stock 2" wide and 4" long and 1' deep

Hi, I am baffled as to how to add a shape to the top of a piece of wood 2" wide and 4" long and 1" deep. So how do I make and apply a shape to the top?
Thanks for any help and I apologize for not being able to describe this any better. I have bobcad version 26 and have seen youtube videos on how to do this in Vetrics and Aspire and it appears to be simple there. I think I am missing something basic. I have watched bobcad videos on youtube and am more confused after watching them.
Mark,

Are you talking about making something out of another piece of wood and attaching it? Or did you want to carve a shape on part of this little piece of wood? If it's the latter, holding it down firmly s going to be one of your major concerns. Often what's done is to use a larger piece to start with, to give you something to hold onto, and cut it down to the desired size afterwards.