Arduino is a good entry-electronic production, with motor expansion board can be a good robot development platform. Here a motor can drive a variety of simple to a slightly complex projects full function expansion board.
This is a common DC motor drive module, L293D the chip small current DC motor driver chips. The pin is made Arduino compatible, convenient enthusiasts quickly Arduino-based development.

    L293D is a monolithic integrated, high voltage, high current, 4-channel driver.
    Basically this means using this chip you can use DC motors and power supplies of up to 36 Volts, thats some pretty big motors and the chip can supply a maximum current of 600mA per channel, the L293D chip is also what’s known as a type of H-Bridge.
    The H-Bridge is typically an electrical circuit that enables a voltage to be applied across a load in either direction to an output, e.g. motor.
    2 interface for 5V Servo connected to the Arduino's high-resolution dedicated timer - no jitter.
    Can drive 4 DC motors or 2 stepper motors or 2 Servo.
    Up to 4 bi-directional DC motors with individual 8-bit speed selection.
    Up to 2 stepper motors (unipolar or bipolar) with single coil, double coil or interleaved stepping.
    4 H-Bridges: per bridge provides 0.6A (1.2A peak current) with thermal protection, can run motors on 4.5V to 36V DC.
    Pull down resistors keep motors disabled during power-up.
    reset button.
    2 external terminal power interface, for seperate logic/motor supplies.
    Tested compatible for Arduino Mega, Diecimila & Duemilanove.

Specifications:
    Model Number: L293D Type Drive IC
    Supply Voltage: 1.5V-6V
    Dissipation Power: 1W-6W
    Operating Temperature: -40C ~ 125C
    Lead Free Status: Lead free / RoHS Compliant
    Maximum Operating Temperature: -40C ~ 125C
    Size:6.8cm x 5.5cm x 2cm - 2.68inch x 2.17inch x 0.79inch.

Document Resources:

L293D DataSheet
Arduino Motor Drive L293D Shield Tutorial

Package Include:
1 X L293D 4 Channel Motor Driver Board Shield