Solder each motor with a black and a red wire and attach them with the chassis.
Attached the motors to the base of the car. Join the left side motor wires together as: red wire --> red wire and black wire --> black wire, similarly join the motors on right side together as: red wire --> red wire and black wire --> black wire
Add the Wheels to the motors
You can also view the video below as a guide
The Motor driver will be the back of the car. The Motor driver will have two connectors, one for Motor A and another for Motor B.
Looking at the car from behind, connect the Left motors to Motor A and the Left motors to Motor B.
Remember that the two left motors will connect to a single Motor A and two right Motors will connect to a single Motor B on the motor driver
Connect the jumper wires as below:
Please remove the jumper from ENA and ENB on the motor driver
Motor driver ENA -> PIN 9 on Arduino Board
Motor driver IN1 -> PIN 8 on Arduino Board
Motor driver IN2 -> PIN 7 on Arduino Board
Motor driver ENB -> PIN 3 on Arduino Board
Motor driver IN3 -> PIN 5 on Arduino Board
Motor driver IN4 -> PIN 4 on Arduino Board
Connect the battery pack positive wire to the VCC / 12V terminal of the motor driver
Connect the battery pack negative battery to the GND terminal of the motor driver
Connect a jumper from the VSS / 12v terminal on the motor board to the VIN on the Arduino board. Connect another jumper from the GND on the motor driver to GND on the Arduino board
Connect the Bluetooth module as shown below
Now you are done with the car assembly. Next you need to upload the code to the Arduino board, download the App and test.