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
While prepaid labels don't expire quickly, it is best to use them within two to four weeks to ensure rates remain valid.
Print the label on a standard printer (paper or sticker) and securely tape it to the package.