If you want to design a computer operated robot, first you must have knowledge of C-programming, this language is the one used for interfacing (to control ports of your computer, ex. printer, serial, parallel, usb, IR).You can then connect devices on them like relays, servo motors or any other actuating devices(basically the building blocks of robots) that will derive signals from the said ports. If you have the resources you could also try investing on PLCs and microcontrollers (the very core of automated manufacturing)