The motors will controlled by motor driver which is connected to Arduino Nano.The MOTORS will attach on the OUTPUTS of Motor Driver. Then, attach IN1, IN2  ( as motor 1 )  and the IN3, IN4  (as motor 2) with the PWM pins  of Arduino.The ENA of motor driver controlled the speed and they'll also connect with PWM Pin of Arduino.Now, Giving electric power to motor Driver to provide power in Arduino and Motors. There are three pins, 12-V, 5V and GND. 5V will attach on 5V of Arduino and GND will attach on GND of arduino Now we provide power in Motor Driver. Connect an ADAPTER 12-V connect +ve (red) wire with 12V and Connect-ve with GND of  MOTOR DRIVER  (black).Now the power will given to MOTOR DRIVER  and it gives 5V to Arduino.