======setup()   ======

The setup() function is called when a sketch starts.  Use it to initialize variables, pin modes, start using libraries, etc. The setup function will only run once, after each powerup or reset of the Arduino board.

===== Example   =====
 <code arduino>
int buttonPin = 3;

void setup()
{
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

void loop()
{
  // ...
}
 </code>


Source: arduino.cc