How do you make 2d images into 3d models?

You would contruct the 3d object from scratch in a 3d program, the 2d images would be used for graphics reference. If they are orthographic images, they can be used in the program's backdrop for the Top, Side, and Front or Back viewports to assist in modeling. The modeler then uses planes called "polygons" that are held together with points, to create the shape of the object. Once the model is created, animation textures are added on top of it to give it it's color.

If you want to turn a 2D image into a 3D model yourself, not just a general idea of how its is done, you would first have to learn modeling starting with the very basics of 3D and the basic tools of a 3d program. 3D modeling is a very involved process and is too complicated to explain in one answer or in words alone. You can get a free trial for Digital Tutors, they hav great tutorial videos, and even have a section titled "Beginner's Guide to Modeling in 3ds Max" that will teach you how to model from the complete basics.