This board is designed to allow you to control high power devices that only have a single polarity. Things like heaters, fans, solenoids, and even motors (you can only turn them in one direction, however.) It takes PWM (pulse width modulation) inputs from a microcontroller such as an Arduino, and amplifies them into high power outputs. It has 3 channels on each board, and can drive up to 5 amps on each channel with the proper heatsinks.