As with QR code generators, you have an abundance of QR code readers to choose from. The one featured here is: just a simple, free app. This one also scans traditional bar codes, in case you need that.
There’s virtually no setup at all. Just open the app and immediately see the four-corner frame on your screen, ready to seek out codes. 
Although you will ultimately use a QR code reader for more practical purposes, when you first set yours up, I would encourage you to play around with it. Scan a cereal box. Find QR codes in magazines. Look for them online. The wonder you feel when you start walking around scanning everything in sight—and they all work!—that’ll make you start feeling like a tech guru in no time.