The setup() function is called when your program starts. Use it to initialize your variables, pin modes, start using libraries, etc.
int buttonPin = 3;
void setup()
{
beginSerial(9600);
pinMode(buttonPin, INPUT);
}
void loop()
{
if (digitalRead(buttonPin) == HIGH)
serialWrite('H');
else
serialWrite('L');
delay(1000);
}