Create your prototypes. In other words, draw your little funky cars. Remember that Pixar cars developed by John Lasseter are anthropomorphic. Place the "eyes" of your cars on the windshield, not on the headlights. Draw their tires as hands and feet. A Pixar "car" can be a train, truck or an airplane.
Use computer-aided design (CAD) to create your 3D model. Your Pixar car will look more like an engineering technical drawing. But not for long! Since your characters are not humans, the car parts (windshields, headlights, tires) become their body parts and subsequently your animation variables or avars. The more avars you use, the better. Your little cars will look animated and alive.
Altering the values of avars over time creates realistic motion. Make your cars move from frame to frame. Place avars at strategic points and let your computer interpose. This process is called keyframing. It is the simplest form of animation. You only need to show the "key" frames, which describe the alteration of an object. All additional transitional positions can be figured out from the "key" frames.
In 3D animation, all the frames have to be rendered. It means that your 3D wire-frame model will transform into 2D images with 3D photorealistic effects after your modeling is finished. You cannot create a photorealistic image on your home computer, so you will need a "rendering farm" where a large number of graphic workstations are networked together to proficiently act as a giant computer. The end result of working with the CGI giant will be your computer-animated movie about anthropomorphic cars, which will closely resemble a Pixar 3D film.