You will have to do this by first getting a bar code font for excel and a USB scanner so that you can attach it to your computer.
You can enter bar code fonts in Google search and download one for the type of bar code you are scanning. This will give you the ability to scan and have the cells populate with the bar code number that your scanning.
The next step with be to do a look up function (vlookup, or index,and match) with the scanned number against your master file to populate your form with the item description as you scan.
Hope this helps