It's not the quickest method, but if you're only shipping a few packages, it'll suffice. Simply go to the carrier's website, fill out the shipping label template, and save or print the file. Is it ...

How to Send a Shipping Label by Email. If your customer needs to return an item, and you have chosen to pay for the return shipping, it will be necessary to send him the label.

You can print a shipping label on eBay and send out items you've sold via standard USPS mail, or through FedEx and UPS. Here's how to do it.