QR codes seem to be used for everything in Korea?

QR codes really are everywhere here. To scan them you usually don't even need a separate app — the default camera on most phones reads them, but KakaoTalk and Naver both have a built-in QR scanner (look for the code icon in the search bar) that locals use constantly. They're used for menus and ordering in restaurants, mobile payments (KakaoPay/Naver Pay show a code you let the cashier scan), checking in, sharing KakaoTalk contacts, Wi-Fi, tickets, and product info. The main thing to know is the same as anywhere — don't scan random codes on stickers or unsolicited texts, since scam codes exist, but official ones in stores and apps are safe and make daily life really convenient.