Why, oh Lord, why do I feel like answering?
Well, I guess the first step would be to obtain some 3d modelling software. The better the software, the more expensive it is. You can end up with software worth a few thousand dollars.
Of course I got no clue what the Devs are using, though I guess they might tell you.
The only 3d modelling software I know which you can obtain for free is gmax which has been discontinued in 2005 and is therefor available for download. All you need is to register at their site in order to achieve an activation key. Maybe that is a good startup to learn the ropes of modelling.
http://www.turbosquid.com/gmax