Discover devices on the same network?

Question

Computer networks

I want to write a program that can be used to send files to a PC from a smartphone. I know that there are ready-made analogues, but it’s purely practical for me
How it should look:
1. Open the application on a PC
2. Open the application on a smartphone
3. The application on a smartphone should display a list of available devices where my application is installed
4. Select, connect
I specifically want to know how to organize this detection and connection, in which direction to dig. Thanks

Answer 1

1. write a server that will know the list of active devices and tell clients about it.
2. UDP broadcast
3. something else - not like everyone else. :)