Where do I create users for Cloud Softphone?

You don't create users for Cloud Softphone, the users are created on your SIP server, not by Cloud Softphone or the web portal. There is a test account section that will create QR codes for those accounts automatically and you can create more QR codes for other users here: https://providers.cloudsoftphone.com/qrgenerator/index

But this is not creating a user. The QR generator is just a tool to make logging into the app easier, the actual credentials for the SIP account still need to be created by you on the server-side.