Communication between Arduino and XBee
Check out https://learn.sparkfun.com/tutorials/xbee-shield-hookup-guide/example-communication-test
Essentially you need to set up Software Serial for your xbee to communicate on a couple of digital pins, instead of using hardware serial. When using hardware serial (the RX and TX pins) only one device works on it at a time, hence why you can't use the xbee and the serial monitor at the same time.