Trying to track inventory using a barcode scanner in Excel

ok...I have a craft business with several different kinds of homemade dips and marinates. Inventory to restock has been an issue. What I am trying to do is at the craft shows I would like to scan barcodes from the back of the items so that it will automatically deduct from my inventory so I can know immediately what I need to restock with out having to manually count each bin after every show. I have set up a spreadsheet, created the barcodes with the barcode font 30f9 and now I am stuck. I need some help with the formula etc so that when I scan during a purchase it will automatically update my sheet. I know a little more than basics but this is a real challenge. Step by steps would definitely help. I have attached my spreadsheet so you can see what I did so far. ANY help would be greatly appreciated.