I think I get it.
From the Relay to the Arduino:
Ground => Ground Arduino
5V Vcc => 5V Arduino
Signal => Pin Number 13, Arduino
From the Relay to the Computer:
NC => Power Switch (6)
C => Power Switch (8)
The for the code:
void setup() {
pinMode(13, OUTPUT);
digitalWrite(13, HIGH);
delay(500);
digitalWrite(13, LOW);
}
void loop() {
// Nothing
}