Real simple to use: The simplest way of explaining how this little board works is this: You connect the power for the device you want to control to the Vin and GND. You connect your device to the V+ and V- screw terminals. When the SIG line is HIGH, a little LED lights up, and the GND is connected to the V-. When the SIG line is LOW, the LED turns off, and the GND becomes disconnected to the V-. The V+ and Vin are continuously connected.