Hello and welcome,
One serial port is enough for bi directional communication with JY MCU BT module (I use it, model HC-07)
Here is example code:
Serial.begin( 9600 );
// Receive string from PC
if ( Serial.available() > 0 )
static char input;
static uint8_t i;
char c = Serial.read();
if ( c != '\r' && i < 64-1)
input[i++] = c;
input[i] = '\0';
i = 0;
// Send a message back to PC
sprintf( output, "String received from PC: \"%s\"", input );
Serial.println( output );
Make sure the BT module is paired with your Bluetooth USB dongle. Just power the BT module and search for new BT devices on your PC.
In the Arduino IDE, Tools menu, set the COM port to the one used by your Bluetooth USB dongle.
In the Arduino IDE's Serial Monitor, set Line Ending to Carriage Return.
You also have to set the Baud speed (in Serial Monitor and in the code) according to your BT module's configuration (default is 9600)
Also, since you don't provide schematic of your wiring, make sure the Arduino's RX go to the BT's TX (and so Arduino's TX, to BT's RX. You should also use a voltage divider for the RX of the BT module because it's not 5V tolerant.