Change field value based on drop down list selection

Let me start by saying that I consider myself a complete rookie when it comes to this program but I am learning. I have a drop down box that contains two choices (White or Bright White) Based on the selection in the drop down box I would like to change a field value to reflect the appropraite part number (Alpha numeric if that matters). I will have 10 fields that will be an either/or value based on the selection. I have searched the forums but without understanding the terminology yet it is hard to find the answer.

Thanks for any help.

Wayne