Edit the row specified by key column(ID)

Hi,

I'm excel beginner,and I'm facing a problem I cannot solve.
I want to enter some values(IDs,numbers) in rows of one sheet,and (immediately or on button click) the corresponding row(by ID) in the other sheet to be modified.How can i do that?

More detailed explanation
I attached a very small .xls example of what I'm trying to do:
- I have two worksheets,one is a simple product list,other a simple order list
- Problem: in the order sheet i select product ID (from a list),and number of products i order; in products sheet total number of that product should be reduced for the number of products that are ordered.
(for example,if i had 100 shirts in products sheet,when 10 shirts are ordered in order sheet,90 should be left in products sheet).

One more thing,in the order sheet i can order hats first,then shirts,then sneakers,so random order-i dont know what is ordered in which row.

I guess I need some macro to do that...

So if someone can help me?

Thanx in advance.