A QR code stores information as a matrix of black squares on a white grid, which can be read by devices like smartphones. These codes encode data such as URLs, contact information, or product details through patterns that represent binary code. When scanned, the QR code decodes the information, directing users to websites or displaying text. QR codes are popular due to their ability to quickly convey information without requiring manual entry, making them efficient for marketing, payments, and various applications in consumer engagement.