A minimal page with Flask (Python) just to test Socket IO

I am new to Flask and Python and I want to develop an application with real-time bidirectional communication between clients and server. I was told that Flask(Python framework) is good for this and that I need to use Socket IO.
However, it looks like that I cannot implement Socket IO in my test application. The server does not receive messages client sends through socket.
Please help me understand the reason. I can show you the code and if required, I can let you work on it or create a minimal test page on my server. Something very simple that for example 2 users can connect the same page and when 1 says "hello", the other sees instantly. Or something like that. I just need to understand real-time communication in Python and Flask through an example.
Thanks