Writing Serial code to read message

Can I ask what is the code require in arducopter 3.2.1 to be add, to read certain message sent from XBEE telemetry.

For example, i got an arduino board and an XBEE connected to the ground control station. when the arduino board voice command and it will then ask the XBEE to send a message from GCS to the XBEE in the uav “Move” for example, what command should i use to check the message written?