I am by no means good at electronics or electrical stuff. I have recently got into the hobby by working on my own personal project. I want to be able to control a 12 volt servo motor that takes a 12 volt signal with an arduino PWM pin. I have tried using a tip120 transistor by following this tutorial: http://bildr.org/2011/03/high-power-control-with-arduino-and-tip120/ however I'm just not sure how to connect the tip120 to my servo motor. Any suggestions?
Connect the servo just like the light bulb is. The PWM signal on the Base of the Transistor will control your servo as if it was directly connected to the Arduino.
Actually, the title of your question is right but the chosen circuit for that need is wrong at all. That circuit won't work, because the control signal needed for a servo motor is omitted in that circuit. Servo motors do need that control when it is controlled by Arduino. The PWM signal will be sent to the servo motor and a potentiometer mechanism is there find its current position and according to the incoming pulse, the servo motor will move to the desired position.
If you need to control the motor with 12V PWM signal, then you need a level shifter circuit of 5V PWM signal to 12V PWM signal. Here is the simple circuit for that need.
Keep in mind that this circuit inverts the logic level of the input (i.e) when an input is high, then the output will be low and vice versa.
When you see the graph, an aforementioned concept can be understood.
Actually, I have found this good circuit from here and experimented it with multisim.