Excel formulas

If I have a stock list and a picking list in different wookbooks, and in the picking list I had to enter a code and quantity, and when I did that I wanted it to look for that code in my stock list, and remove the quantity that I entered in the picking list from my stock list.
for example:-
Code Quantity
taglarge 18
I would want it to look for that code in my stock list then remove the quantity for that item from my stock. so I can save time filling in two forms all the time.
THX hope you understand that and hope someone can help.