int Led = 7;
int btn = 6;

void setup() {
  // put your setup code here, to run once:
pinMode(Led, OUTPUT);
pinMode(btn, INPUT_PULLUP);
digitalWrite(Led, LOW);
}

void loop() {
  // put your main code here, to run repeatedly:
if(digitalRead(btn) == LOW ){
digitalWrite(Led, HIGH);
delay(3000);
digitalWrite(Led, LOW);
}
}