Thanks a lot! Glad that you enjoyed playing Knightin' :)
QR codes contain solutions for the puzzles. You might've found rooms with lots of blue symbols on the floor. QR codes tell you which of them have to be activated.
So do I need a smartphone to scan the QR codes?
QR codes contain puzzles' solutions. You can use them if you haven't found another hints or can't figure them out. You need a smartphone to scan QR codes or you can make a screenshot and use an online scanner.