Two pairs of buttons on either side of the remote’s backside send data for channels 5 and 6 respectively.
The swappable RF transmitter crystal module is plugged in at the top in the center. All remotes ship with a transmitter/receiver pair for 75.410 MHz / Channel 61. Other frequency modules are available for purchase separately so that robots can operate in the same physical area or so that multiple remotes can be used to control the same robot.
In the dead center of the back of the remote (covered in the photo by a protective rubber flap) is a tether port for connecting the remote control directly to the microcontroller via RJ-10 cable. This is useful for troubleshooting especially if you think the the receiver module may be part of the problem.