Paypal will let you print labels without having an underlying Paypal transaction. It has limited international postage functions, though (only the expensive ones) unless you are shipping an Ebay package.

Ebay will only print labels for Ebay transactions.

You can create a free account at the post office (USPS.com) and print labels from there using the "Click-N-Ship" feature. Of course, you will need a credit card: https://cns.usps.com/

You can also use Stamps.com, but they charge a subscription (there are some free offers for Ebay sellers, but if you're an Ebay seller you might as well use Ebay's shipping program).

Hope this helps with Step #1!