How to organize WiFi multiplayer on android?

Question

Android

Please explain to someone how WiFi multiplayer works in applications.
The Internet is full of tutorials on this topic. For example, with multicast DNS it is very easy to connect 2 devices on the same LAN. But it turns out that both the client and the server must already be connected to some kind of network (that is, some other device is needed that would distribute this network). If the server turns on the modem mode, then it will no longer be able to connect to its own network and, therefore, nothing works anymore.