void setup() {
 // put your setup code here, to run once:
 pinMode(3, OUTPUT); //THIS IS THE RED LIGHT
 pinMode(4, OUTPUT); //THIS IS THE BLUE LIGHT
 pinMode(2, OUTPUT); //THIS IS THE GREEN LIGHT
}
void loop() {
 // put your main code here, to run repeatedly:
 digitalWrite(3, HIGH); //this will turn on red
 delay(2000);
digitalWrite(3, LOW);  //this will turn red off
 digitalWrite(2, HIGH); //this will turn on blue
 delay(2000);
 digitalWrite(2, LOW); //this will turn blue off
}