This page generates new QR-codes that don't point anywhere yet. That means you don't have to think about which code points where, until after you have placed them.
When ready, all you need to do is scan each code and enter a web address.
Try it on the upper left QR-code from below in this window:
After you have linked a QR-code to an address, scanning the code will take you directly to the linked web page.
If you want to change the address of a specific QR-code later, use the link under the QR-code you want to change, except with "/edit" added to the end like this:
Or type the code here: