You would use the Servo Library; sending it a signal of "0 degrees" with Servo.write (or 900ms with Servo.writemicroseconds) will turn it full speed in one direction, and "180 degrees" is full speed in the opposite direction.
When you send it a signal for 90 degrees the servo should be stationary. If it's not THEN you use the external potentiometer and adjust it until it stops. To emphasize, the potentiometer is only there to fine tune the midpoint; in all other respects it's just like any other servo.
For the red/black/yellow wires on the servo, the red connects to 5V, black to GND, and the yellow to one of your digital pins on the Arduino (see the documentation).