This shield have two separate channels, called A and B, that each use 4 of the Arduino pins to choose the rotation direction, vary the speed, fast brake or sense the current that is flowing through the motor. In total there are 8 pins in use on this shield. You can use each channel separately to drive two DC motors or combine them to drive one unipolar stepper motor. The shield can supply 2 amperes per channel, for a total of 4 amperes maximum.
This shield has the 1.0 standard pinout that consist in 4 additional pins: 2 of them placed near the AREF pin, that are used for TWI communication, and the other 2 are placed near the RESET pin. The IOREF pin is used to adapt the shield to the board on which is mounted. The last one is not connected and is reserved for future uses.