Easier to create label, pay online
I am anything but a shill for the postal service, but really folks, have you not hear you not heard of USPS.com?
Visit the site and you can create a label to mail most any package, paying for your postage with a credit card and creating a label to affix to your package.
And then, if you don't want to schedule a pickup by the post office, you take your package, march into the post office, place the package on the counter and you are on your way. No waiting in line or worries about how you will pay for it. And if you like you can track the progress of the package until it is delivered.
Nothing more simpler!