My suggestion would be to first ensure that you can control the 2 motors with the Arduino. One Arduino digital pin to each of the motor control input pins and a common GND connection.
Write a small program to move the motors in each direction for a period then both motors at the same time. Do NOT use delay() for the timing, use millis() instead. See Using millis() for timing. A beginners guide, Several things at the same time and look at the BlinkWithoutDelay example in the IDE if you are not familiar with the technique.
As a matter of interest, what happens if a motor is commanded to go in both directions at once ?