Your question is too general. This forum is designed to help folks work
through issues, syntax, strategy, etc. There is not space to go through the
strategy at that level.
What I will say, is that many bar code readers present themselves as
keyboard replacements. If you have an application, you can typically click
into a text box or combo box, actuate the bar code reader, and it will "type"
the bar code translation into the box for you.
Inventory is an application that has "been done" a million times. Google
"Inventory Management Access", and you're likely to find a dozen pre-written
apps you can buy, use, or use as a starting point.