When you buy a label online, UPS often provides a mobile UPS Shipping QR code. You can show this at a UPS Store, and they will print the label for you on-site. UPS Shipping Supplies & Physical Labels
If you are looking for physical, blank labels or specific carrier stickers to use with your own printer, you can find them from various retailers: Create and Print Shipping Labels | UPS - United States
The most direct way is to use the UPS website to generate a PDF label that you can print at home.