QR Codes are like barcodes but are able to hold a lot more information. Often they are used to share web links. You can use your smartphone to access the information behind the QR Code. To access the information you will first need to download a QR Code reader (if your phone doesn’t have one built-in). You will then need to use your camera pointed at the QR Code, and it should reveal the link.
For Apple iPhones and iPads: https://support.apple.com/en-us/HT208843
For Android try https://lens.google.com/