int8_t led = 0;

void setup() {
   // Serial.begin(); //this isn't needed, it is pre-initialised , otherwise you could uncomment it to test
   pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  if(Serial.available()) {
    char c = Serial.read();
    Serial.print("hello ");
    Serial.print(c);
    Serial.println();
  }
  led = ~ led & 1;
  digitalWrite(LED_BUILTIN, led);
  delay(500);
}