That is offering you to print your shipping label for those who choose to pay for their shipping through Paypal. That's what you do when you want to schedule USPS to come pick the package up from your house so that you don't have to go to the post office.
I didn't use that for the longest time. I always took my packages to the post office myself and paid my shipping there. But now I use Paypal to pay for and print my shipping and I have USPS pick my packages up from my house. Saves me almost $4 worth of gas not having to go to the post office.
If you ever want to try that method of shipping when you click to print the shipping label it will walk you through what you need to do but you will need a scale that can weigh your packages in ounces, like a kitchen scale, or a digital bathroom scale if it is a big item to weigh it in pounds.
Then you print it our, tape it to your package (delivery confirmation is free when you ship it that way too) then go to USPS.com and schedule a front door pick up. Once you do that one time, you won't ever get out and go to the post office again. Saves me a lot of time and trouble.