QR Code also known as the quick response code was developed as an alternative to the Barcode. QR codes can embed data in the structure such as URL, address, name, encrypted content, login details, payment address, checksum etc.
QR code can be read by the mobile based scanners. In case of desktop and tablets you can also use the default apps in the system to scan the picture that you take in the desktop. And the same applications can then show the respective data embedded in the code.
QR code are different from the bar code due to it's dimensional use like numberic, alphabets and other content. So with barcode you can limited amount of data can be read but in case of QR code you have lot more flexibility.
Depending on your usage, you can generate the QR code and let the scanner do the remaining work. In case of payments, say you scan the QR code of the payee from the app and then let the app search it's name and then pay that person. So this is one use case being done by the UPI based apps.