The 5V 1 Channel Relay Board is equipped with one 5V DC-controlled relay that can control loads of up to 125/250V AC @ 10A or 15V DC @ 10A each. It is convenient for controlling external loads. Unlike transistors used for switching, relays use metallic switch contacts to prevent power loss and heating in transistor switching circuits. It includes a relay driver transistor and a built-in opto-isolator on the inputs, requiring less than 5mA on the logic control pin to drive the Relay Board. If you have different development boards like Arduino, you can control the relays using any digital output pin. When power is applied to a relay, it draws approximately 70mA from the Vcc pin. When power is supplied to all eight relays, the total current draw is approximately 600mA.
NOTE! : When controlling 220V AC Mains Voltage in your projects, don't forget to take necessary precautions.