LED: We set one of the pins on the Arduino HIGH which outputs to a circuit which is an LED in line with a resistor to limit current.
Motor: We set up an NPN transistor as a relay. In this configuration we have power supplied to the motor and the path to ground is controlled by the transistor. Setting the port high allows the transistor to connect the motor to GND.
Buzzer: Set up in the same fashion as the motor.
Pressure Sensor: The pressure sensor acted like a potentiometer. While the sensor was not pressed it had so much resistance that it acted like an open circuit. When the sensor was pressed is lowered the resistance and acted like a short circuit which made the voltage on the port readable.