In order to build a robot its is necessary to be able to program a microcontroller and know the basics of electronics(which motor to use and how an interface has to be created between microcontroller and motor).
A stepper motor is employed to achieve moment of the robot and stepper motor is controlled by the microcontroller. To achieve movement in different multiple stepper motors are employed. One motor to move forward and backward, other motor to move right and left.
The concept is entirely simple.
Make yourself comfortable with some designs available. Then you can start designing on your own. All the best chap.