And would like to connect multiple Poti on Arduino MEGA and the XBEE module to send Arduino UNO and several servo control.
So with potentiometer 1 servo 1
with potentiometer 2 servo 2
with potentiometer 3 servo 3
etc. .. Taxes!
Suppose that you connected TX of the UNO to RX of the Mega, and RX of the UNO to TX of the Mega, and connected the grounds. You'd use Serial.print(), Serial.println(), or Serial.write() to send the data and you'd use Serial.available() and Serial.read() to receive the data.
Well, guess what. You'd use EXACTLY the same code with the XBees in place, instead of the wires.