Current sensing: 1.65V/A. Operating Voltage: 5V to 12V
Motor controller: L298HN, Drives 2 DC motors or 1 stepper motor
Max current: 2A per channel or 4A max (with external power supply)

Power:

The Motor Shield must be powered only by an external power supply. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. 
To avoid possible damage to the Arduino board on which the shield is mounted, we reccomend using an external power supply that provides a voltage between 7 and 12V.
If your motor require more than 9V we recommend that you separate the power lines of the shield and the Arduino board on which the shield is mounted.
This is possible by cutting the "Vin Connect" jumper placed on the back side of the shield. The absolute limit for the Vin at the screw terminals is 18V. The shield can supply 2 amperes per channel, for a total of 4 amperes maximum. 

Motors Connection:

Brushed DC motor. You can drive two Brushed DC motors by connecting the two wires of each one in the (+) and (-) screw terminals for each channel A and B. In this way you can control its direction by setting HIGH or LOW the DIR A and DIR B pins, you can control the speed by varying the PWM A and PWM B duty cycle values.
The Brake A and Brake B pins, if set HIGH, will effectively brake the DC motors rather than let them slow down by cutting the power. You can measure the current going through the DC motor by reading the SNS0 and SNS1 pins.
On each channel will be a voltage proportional to the measured current, which can be read as a normal analog input, through the function analogRead() on the analog input A0 and A1. For your convenience it is calibrated to be 3.3V when the channel is delivering its maximum possible current, that is 2A.

Dual Channel DC Motor Driver Shield Expansion Board L298NH Drive Module for Arduino UNO R3 MEGA2560