-catch and box the birds
-weigh the package
-once you know the weight you go and fill out the shipping information and such on USPS website. I usually add a few ounces to the weight just to be safe.
-after completing the information you pay for the shipment and then you print out the labels (including the receipt to bring to PO)
-finally you bring the birds to the PO and they will weigh the box just to make sure the weight is correct and you are all set.
The first time I used Click-N-Ship the person at the PO did not know what to do and they were trying to charge me the full price. Just make sure you print everything out and show it to them. It is convenient just to drop the birds off at the PO.