Connect a resistor and led to the arduino and load a program that will make the led blink.

/*
  blink
  Make led blink
*/

// Use a variable to set the output pin
int led=12;

void setup() {
  // initialze pin as an OUTPUT
  pinMode(led, OUTPUT);
}

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

• Does it matter which way the resistor or led are connected?
• Could you use another variable for the delay?