I don’t know, if there is anything different with the FP3.
As I know it, you need an App and a camera.
Apps can be found on f-droid.org as well as in the playstore.
Here are just 4 examples from f-droid:
- QR Scanner (Privacy Friendly)
- Barcode Scanner
- SecScanQR (The QR code scanner/generator that cares about your privacy)
- Obsqr (The most lightweight QR code reader)
Searching on f-droid you will find much more apps.
I have just very briefly tested the first two on my FP2 and they seem to work.
Edit:
I just changed the first link to the english version.