How can I scan QR codes on iPhone?

iOS 11 added a QR code scanner to the iPhone Camera app, how do I use it?

The QR code reader should be on by default if you have iOS 11 installed. Simply focus on a QR code and your iPhone will notify you that you can go to the website on Safari, or whatever other action the QR code offers (join a Wi-Fi, email somebody, etc.). If for some reason it isn't on, head to Settings -> Camera and toggle on "Scan QR Codes."

How to use the QR code scanner on iPhone and iPad.