There is a popular tutorial on how to parse the bytes of serial communication. However, it is quite time-consuming to implement a serial communication parser from scratch. SerialTransfer and ...

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.

In the example sketch you can replace the Serial Printf for ARDUINO_USB_SUSPEND_EVENT and ARDUINO_USB_RESUME_EVENT with a digitalWrite to a LED to see the behavior without having access to the serial.