The Motor Shield is based on the L298,
which is a dual full-bridge driver designed to drive inductive loads
such as relays, solenoids, DC and stepping motors. It lets you drive
two DC motors with your Arduino board, controlling the speed and
direction of each one independently. You can also measure the motor
current absorption of each motor, among other features.
The Shield comes as kit with premounted SMD parts and the THT connectors have to be soldered by the you.