How to start with local offline multiplayer?

I have scraped the internet on this question. I have been developing basic unity games since an year now, and want to learn some networking now. I am trying to learn to establish simple networking first, where multiple phones are connected to same wifi network, or one phone creates a hotspot and the others connect to it. How can I establish multiplayer on it? Or simply exchange data/messages? Where do I go from here?? Thanks