Major carriers like UPS and FedEx offer similar tools to create shipping labels directly on their sites.
If you don't have a printer, use the USPS Label Broker® tool to receive a QR code, which a Post Office kiosk can print for you.
Shipping online (e.g., via USPS Click-N-Ship®) often provides lower commercial rates than paying in person. To give you the best guide, are you looking to ship: A small letter/envelope? A small package (e.g., for eBay)? Large, heavy boxes? Also, do you have a printer available at home? How to Prepare & Send a Package - USPS
A return address is required for all prepaid labels.
Input sender and recipient addresses, and package details into the online tool.