A QR code is a compact way to hand someone a link, a block of text, or WiFi credentials without them typing anything — point a camera, and whatever's encoded opens or displays automatically. The technology itself is simple; what trips people up is encoding the wrong kind of content for what they actually want to happen when it's scanned.
The most common mistake: treating a QR code as if it always opens a website, when what it actually does depends entirely on what was encoded into it. A URL opens a browser. Plain text just displays as text on the scanning device. A correctly formatted WiFi string lets a phone join a network directly, skipping manual password entry entirely — genuinely useful for anyone who's ever had to read a WiFi password aloud letter by letter to a guest.
QR codes have built-in error correction, meaning a code still scans successfully even if part of it is damaged, dirty, or has a small logo placed over the center. This is a genuine, useful feature — but it has limits, and a cleaner, higher-contrast code will always scan faster and more reliably than one relying heavily on that error correction to work at all.