IMO, the easiest way would be to name the specific ranges in the spreadsheet.
For example, if you had the following table:
Product | Stock |
Shampoo | 15 |
Soap | 13 |
I would name the cell with the number 15 in it something like "ShampooStock" and the cell with the number 13 in it something like "SoapStock".
Then, whenever an order is placed, you access the sheet and the named range like:
Worksheets("Products").Range("ShampooStock") = Worksheets("Products").Range("ShampooStock") - NumberOrdered