Can you please give some detailed insights, how this HTTP communication is used in my case (just consider App) and how I can I send the required data from the robot to an external PC? Does it is possible to change Digital output or user output from python script?
I pretty much already said everything. An HTTP GET command from Python (or a browser, or any language) to the correct URL on the robot can trigger a KAREL program to run once, and the KAREL program can be set up to accept arguments (up to 10) as strings built into the URL, and can build and return a string to the requesting program.
The KAREL program can be programmed to do anything a "normal" KAREL program does. In my use case, various Flags and DOs were set in response to specific arguments embedded in the URL, and status information was passed back in the response string.