Image courtesy of SparkFun Electronics

Use a servo for precise position control (unlike a DC motor). Color scheme vary, but generally the red/orange wire is 5V, the black/brown wire is ground, and the white/yellow wire is the control signal. Servos can consume a lot of power, so consider connecting the 5V wire to a separately regulated 5V supply instead of the Arduino’s 5V power. Unless modified, servos generally have a 180 degree rotation range.

Buy a servo motor from Amazon, SparkFun, or Adafruit.