This is a simple single-channel relay module. Connect power and then switch the relay on by applying a high signal to the "S" pin.
The module has three screw terminal connections connected to the relay that include common, normally open (N.O.), and normally closed (N.C.).
WARNING: The screw terminals and relay solder connections are exposed on the bottom of the board. Caution must be used especially when using this module with high voltages, such as mains power or any voltages greater than 12V. Always disconnect high voltage from the module before wiring or touching the module. When high voltage is supplied to the module be sure to refrain from touching or pointing to any part of the module. Working with high voltages should only be undertaken by experienced individuals.