Servos are the easiest way to start making motion with an Arduino. Even though they don't turn 360 degrees, you can use them to create all sorts of periodic or reciprocating motions. In this project, potentiometer values are read in through an 'Analog In' pin. The values are then used to control the position of a servo motor.
Use a 1kΩ potentiometer and a servo. Connect three wires to the Arduino board. The first goes to ground from one of the outer pins of the potentiometer. The second goes from 5 volts to the other outer pin of the potentiometer. The third goes from analog input 2 to the middle pin of the potentiometer. Connect the servo's yellow wire to a PWM input pin, the red wire to 5 volts and the black wire to ground.