You need to learn how to use one of the 3D design programs.
Many people like Blender
http://www.blender.org/ It can be difficult to learn, but there are many tutorials. I like Anim8or
http://www.anim8or.com/, but its author hasn't updated it for a long time. It also has tutorials. Both programs are free.
There are many other 3D design programs. Some are free. Some are inexpensive. Some are very expensive.