A QR code, or Quick Response code, is a barcode scanned with a mobile phone camera. It contains information such as website URLs and contact details, which open on the user's phone when scanned.
Yes, this is completely free to use.
In Google Forms, click on the purple Send button in the top right corner. This will open a new window with three different options. Click on the link icon, then copy the URL and paste it into this free QR code generator.
There isn't native Google Forms support for this. However, you can send an email when a Google Form is submitted using Lido, the spreadsheet that automates work for you. Learn more here.