I'm in a doubt whether that we need to program the arduino uno when it is used for receiving? the arduino UNO only stack with xbee + xbee shield for wireless connection purpose. Is there any codes to upload to the arduino UNO?
The arduino has no "default" program, unless you count blink which just blinks the LED. It can do nothing until you program it. There is no "passthrough" mode.
is there any sample codes just for tx, rx?
Look in the reference for "Software Serial"