As seen in the diagram below, two momentary pushbutton ... do not link Arduino’s ground rail (Gnd) to the relay module’s ground pin (GND). Otherwise, simply connect Arduino 5V and Gnd, and leave VCC ...

In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...