Type of WiFi network?

Hi! I have a small network problem and I think the people here can help me, since I don't understand even half of the threads underneath hahaha

Context: There is a business Wi-Fi network at my work, said network appears "without password" and anyone can join, but once connected it opens a web page in which it requests a password and only after authenticating on said page does it give you Internet access.

Question 1: What type of network is it? That is, where can I start to learn how these networks are built?

Question 2: There are some devices that the authentication web page are not "invoked". How can I know the IP or URL address to which I should connect?

I tried to do something simple like use nmap to scan open ports and the type of service it offers, but being an enterprise network this is obviously blocked (or is it just that I don't know how to use nmap) anyway, I am stranded. I found an old android device that in the wifi information, it shows what the IP of the web page is, but in modern devices it is not.