You would use a microcontroller on the robot. it looks for a serial command from the receiver, then processes the command accordingly.
1. wireless cam on robot captures image and transmits the image to your PC
2. RoboRealm processes the image and, based on a script you write, determines what serial command to send (for example, based on the image being left of center, send the serial command for turning the robot to the left)
3. Use the Serial module in RoboRealm to transmit that command out your serial port on your PC
4. Use a microcontroller to receive the serial command from your PC and transmit it via the RF Transmitter
5. The RF Receiver on your robot will pick up the signal and send it to a microcontroller on your robot.
6. The microcontroller on the robot will take in the serial command, then based on the command send instructions to your motor controller on how to drive the motors
7. Repeat steps 1 through 6.
All of this is clearly documented on the RoboRealm website under the "Color Object Tracking" tutorial at http://www.roborealm.com/tutorial/color_object_tracking_2/slide010.php