A servo is awesome for controlling an RC car or robot. Inside each one is a DC brushless motor, some gearing, electronics, and a potentiometer. What does all that mean to you? Just tell them where to go and they do the rest. “Move to 45 degrees!” and they just do it. No questions asked.
These 9G servos have a range of 0 to 180 degrees. You tell them where to go by sending a Power Width Modulation (PWM) signal. The Arduino UNO R3, for example, can send 6 PWM signals at once. The MEGA has a huge number of PWM signals.
Put two servos together to make a pan/tilt system for your GoPro. Put three together to make a small robot arm. The possibilities are limited only by your imagination.
These servos have three wires: brown for ground, red for 5v power, and yellow for the PWM signal. Each unit comes with mounting screws and three servo horns that make it easy to attach things to the turning output shaft of servo.