Hi- I ship about 20 packages a week, and I RARELY go to the Post Office. Go to the USPS website
www.usps.com and register for "click and ship." Here is a link to the registration page.
https://sss-web.usps.com/ds/jsps/index.jsp This allows you to print out Priority labels from your own computer, and you can sit the packages out for your mail carrier to pick up at no cost. I have found that some postal workers are not well-informed about this, but you can find all the info online. Normally, carriers can't pick up a package over a pound, but they will if you use this method.
For payment, I use a Paypal debit card #. It's on file with my click and ship acct, so my postage just comes out of my Paypal account. Very handy.
There is no additional charge for any of this, *and* and you get delivery confirmation for free. (There is a small charge if you buy it at the post office.)
The only drawbacks I've encountered are these: they only offer Priority, not first class postage, they don't offer Global priority, and you still have to go to the PO if you want to insure a package. However, about 98% percent of my shipping is domestic Priority, and I rarely need to insure.
If you want to ship UPS, you can do that directly through Paypal, and you get a better rate than if you do it through the UPS website, and a MUCH better rate than UPS over-the-counter. You can print out your postage labels at home and drop them off at a UPS Store, or call for pick-up.