drop down box

[Masterpiece]

I've been reading on this and I still can't figure out how to do it. I want to have a drop down box that can calapse when you select an option. I'll tell you my example that I need:

I have a material column, underneath material I want to be able to choose from a variety of wood species. Like this:

MATERIAL
(PULL DOWN MENU WHERE I CLICK ON AN ARROW)
RED OAK
W. OAK
HICKORY
A. CHERRY
B. CHERRY....ETC.....

I've attached a zipped file of my spreadsheet incase you all wanted to see what I was talking about. I'm brand new to excel so go easy on the design of my spreadsheet .