This is a breakout board for driving DC motors. The board is based upon popular L293D IC that contains two H-Bridge circuits to drive two DC motors independently. You can also drive one Bipolar stepper motor with this driver.
The H-Bridge can accept an external DC power supply up to 30V and can power the motors up to 500mA continous current.
The Inputs from microcontroller are :
IN1, IN2 and E for each motor. A logic 1 on E will enable the H-Bridge and IN1 and IN2 will control the direction of motor rotation.
You can control the speed of motor by giving PWM on E pin.
Making E low will cause the motor to free run under inertia.