What is the principle of operation of Guest access and authorization in WIFI networks?

Question

WiFi

I am specifically interested in Cisco WLC and Cisco ISE, but I will be happy with a simple description of the principles. Because at the moment I can’t put the authorization process in my head.
What I understood:
LAP is authorized on the controller.
LAP broadcasts SSIDs
SSIDs are tied to VLANs
Authorization can be done in the controller or in an external RADIUS server
. What I did NOT understand:
How to organize a network infrastructure in principle (IP addressing and VLANs)
How does an authorized subscriber switch from GUEST SSID to, for example, SSID for employees.
I would appreciate if someone "poke his nose" in a brief description of all this (except for the CCNA tome and the like)