// Bluetooth module used - HC-06

#include <SoftwareSerial.h>
SoftwareSerial BlueTooth(10, 11); // (TXD, RXD) of HC-06
// Connect the HC-06 TX to the Arduino RX. 
// Connect the HC-06 RX to the Arduino TX through a voltage divider.

char BT_input; // to store input character received via BT.

void setup()  
{
  pinMode(13, OUTPUT);     // Arduino Board LED Pin
  BlueTooth.begin(9600);  
  // The default baud rate for the HC-06s I have is 9600. Other modules may have a different speed. 38400 is common.
}

void loop() 
{
  if (BlueTooth.available())
 
  {
    BT_input=(BlueTooth.read());
    if (BT_input=='1')
    {
      digitalWrite(13, HIGH);
      BlueTooth.println("Now LED is ON");
    }
    else if (BT_input=='2')
    {
      digitalWrite(13, LOW);
      BlueTooth.println("Now LED is OFF");
    }
   else if (BT_input=='?')
    {
      BlueTooth.println("Send '1' to turn LED ON");
      BlueTooth.println("Send '2' to turn LED OFF");
    }   
   // You may add other if else condition here. 
  }
}