You can read the state of a button using Arduino and a few lines of code. The actual state is shown in the Serial Monitor window as 0 or 1, 0 meaning the ...

You haven't directly made use of the serial communication between the host computer and the Arduino board. First, I'll describe how to write a basic client/server style program.

While the Arduino family of boards connect to your computer using a USB virtual serial port, the ATmega ones have an actual serial connection on-board.