Circuit 1.3: Hello, blinky World!

Making an LED blink is the hardware-equivalent of printing "Hello, Word!".

Change your circuit to this:

Add this code, save and upload it to your Arduino:

void setup() {
    pinMode(3, OUTPUT);
}

void loop() {
    digitalWrite(3, HIGH);
    delay(1000);
    digitalWrite(3, LOW);
    delay(1000);
}

It's nicer to put your pins into variables at the top.

#define LED_PIN 3
// or int led_pin = 3;

void setup() {
    pinMode(LED_PIN, OUTPUT);
}

void loop() {
    digitalWrite(LED_PIN, HIGH);
    delay(1000);
    digitalWrite(LED_PIN, LOW);
    delay(1000);
}