The two resistors on the far left represent photo resistors. A motor should be connected between the two transistors. If the resistance of the top resistor is greater than the resistance of the bottom resistor the motor rotates counter clockwise. But if the resistance of the bottom resistor is greater than the resistance of the top resistor the motor rotates clockwise. When both resistors are equal the motor does not rotate at all. With this circuit you can make a car that follows light.
