This 1-channel 5V control Single-Pole Double-Throw (SPDT) AC power relay board can be controlled directly via a microcontroller and switch up to 10 amperes at 250 VAC. Inputs are isolated to protect any delicate control circuitry.
The default state of the relay when the power is off for COMM (power) to be connected to NC (Normally Closed). This is the equivalent of setting the relay board IN pin to HIGH (has +5v sent to it).
When you have power connected to the relay’s NO (Normally Open) connector and you set the corresponding IN pin to LOW (0V, or Ground), power will flow in from the COMM connector and out of the NO connector powering your device.