Taking the the value of items from 1 workbook and minusing/a

[VSB]

I am doing a As level coursework on excel. My system is based on a restaurant. I have an order screen which calculates the value of each order (e.g 2 cokes ). I then want to take the items(2 cokes) away from the stock workbook while at the same time adding the 2 cokes and the price to a seperate bill workbook.

Thank you in advance
Vedran

P.S if anyone enjoys making excel projects feel free to do the rest of it for me. I will be happy to provide further information