int ledPin = 4;
void setup() {
  pinMode(ledPin, OUTPUT);      //define ledPin as output pin
}
void loop() {
  digitalWrite(ledPin, HIGH);   // setting the ledPin to high / setting 5V on the ledPin
  delay(200);                   //wait for 200 milliseconds
  digitalWrite(ledPin, LOW);    //setting the ledPin to low / setting the ledPin to ground
  delay(200);                   //wait another 200 milliseconds
}