They mean just what it says, putting a barcode page on top of each package. That's how they can scan and attach the docs to the specific case.
http://www.cic.gc.ca/english/information/applications/spouse.asp
IMM 1344 and IMM 0008 form
Click the "Validate" button at the top or bottom of the form.
Note: Validating the form before printing makes sure that you have answered all the questions. This will help you to avoid delays in processing your application.
A last page with barcodes and a signature line will automatically be created.
Print, sign and date the form.
For best results:
print on white, bond-quality, non-glossy paper and
use a laser printer.
Place the barcode page on top of your package. If you have more than one package, place a separate barcode page on each one.