The CGSLD is a tiny ancillary board that contains a single transistorized LED driver. It is designed to be connected to any output that puts out a voltage that ranges between 0V and over 2V. As presented in the diagrams, the module is designed for gate signals where the LED will have an ON/OFF action.
The PCB is supplied as a strip of 11 boards and the Component Kit contains components for all 11 boards including 3mm Red LEDs and lens mounts.
CGS LED Datasheet and Build Guide