Any text documentation//tutorial to learn about online multiplayer game?

I know there’re videos to learn about create a multiplayer games. But I have an issue watching videos and would like to just read. I does not live where I can purchase a text book so I have to look up online but what I found also not exactly it… or mostly refers back to the videos on YouTube. So, I come here asking for any recommendation on any website/blog/text tutorial that you know.

Here is what I am trying to do:

  1. Actually, it’s not a game but a stamps collection book that people can see other in real-time when they ‘stamp’ another picture into the book. They won’t see drawing lines or any interaction but only once the picture is confirmed to be added into the page.
  2. It will be online; not only a local server and, people can access through their smartphone.
  3. It’s a simple graphic using P5.js like 95% of the whole UI.

What I know and don’t know:

  1. I have worked with Processing and P5.js for years so I know some workaround for visualization but, not so much about the host/server issues.
  2. I have never worked with Firebase, and Node.js.

Thanks a lot!