char command;

void setup() 
{
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  Serial.println("Enter command: 1, 2, 3 to toggle LEDs");
}

void loop() 
{
  if (Serial.available() > 0)//if user enters something, it will reaturn a value > 0
  {
    command = Serial.read(); //Reads 1 Byte

    switch(command)
    {
      case '1': digitalWrite(2, !digitalRead(2)); //Toggle LED Red (1)
                Serial.println("LED1 toggled");
                break;
      case '2': digitalWrite(3, !digitalRead(3)); //Toggle Blue LED (2)
                Serial.println("LED2 toggled");
                break;
      case '3': digitalWrite(4, !digitalRead(4)); //Toggle Green :ED (3)
                Serial.println("LED3 toggled");
                break;
      default: Serial.println("Invalid Command");
    }
  }
}