I guess that it's a DC motor, and the N-channel MOSFET supplies battery power to the motor. The power will be controlled by PWM. The Schottky diode is a freewheel diode to prevent the inductance of the motor windings from blowing the MOSFET when the current turns off. The inductance of the motor windings will mean that when the MOSFET turns off, the current in the motor can't stop instantly. When the MOSFET turns off, the current will run through the Schottky diode instead.