There are some good and bad choices for qr code generators on the web.
My favorite generator is the duckduckgo search engine, just type qr: https://example.com as the search.
The string can be anything; typically you want the https:// part as well.
The chrome browser can also share a qr code.
Chrome needs higher resolution. I think the dino in the middle needs extra error checking.
A bad generator will produce a code that links back to their site which uses a database to redirect to your site. They will help you collect statistics. And if you failed to understand how it works, they will let you know six weeks later that you'll need to pay to keep the link working (which will be cheaper than re-printing your material...)
This project was useful when I was researching: https://github.com/zxing/zxing
Craige