The Arduino Motor Shield is based on the L298 (datasheet), which is a dual full-bridge driver designed to drive inductive loads such as relays, solenoids, DC motors, and stepper motors. It allows you to drive two DC motors with the Arduino board, controlling the speed and direction of each independently. You can also measure the current absorption of each motor, among other features. The shield is compatible with TinkerKit, which means you can quickly create projects by connecting TinkerKit modules to the board.