iRobot Create uses a specific protocol which is implemented by this library. It is called Open Interface (OI) version 2. When instantiating the robot class (iRobot::Create) you have to indicate which stream is used to communicate with the robot.
Typically you probably want to use a serial port device for the communication such as:
The last solution requires the Bluetooth adapter module (BAM).
To communicate with the robot, you need the serial port support. To enable this, you have to use the LibSerial 2.1 library (it library has to be installed on your computer).