BUILD YOUR OWN 3D PRINTED ROBOT
The basic components of the robot are: servo motors, Arduino, and buttons. The buttons are mounted on a circuit board that control the fingers of the hand. When the buttons are pressed, the Arduino reads the value which triggers the servo motor. The servos pull the strings that act as tendons, allowing the fingers to move.
I have put together a wish list on Adafruit containing some of the parts you will need. The robotic hand comes from an open-source, 3D-printable download from a project called InMoov.