I got a RPI4 and I would like to communicate to it from my Android Studio made app. Specifically I would like to start a javascript with node.js on the RPI. So the RPI should be sort of an headless machine controlled with a smartphone.
However, I find it difficult to get an overview of all the options of how to create this communication, and I cannot find a good beginners guide of how to accomplish this.
Ideally it should work without access to internet. From what I can find I should make a local network connection, but I dont know how to do this. Can you help me?