QR codes are made of small black and white squares. They may look like simple patterns, but they hold information.
Computers can read the difference between black and white like numbers. In a QR code, the order of the small squares represents data.
When you scan a QR code with a phone, the camera looks at the pattern. The app checks where the black and white parts are. Then it changes the pattern into words or a URL.
QR codes also have large squares so that a phone can find their direction. This helps the phone read the code even when it is a little turned.