The blurry shots are shutter speed, the shutter is open for so long that any movements you or the object make, will be captured.
As for some bits being blurry and others not, there are two kinds mentioned above.
Laingo is talking about stationary objects and using the different depth of field to throw objects that are further/closer from your focal point out of focus, the amount of depth can be altered by the aperture, the f-number on your camera, on a standard lens, anywhere from 4 upwards.
The other that Giraffe mentions is using a slower shutter so that when the shutter is open, the background/wheels are moving but by moving the camera and keeping the car in the same place relative to the camera, the car remains in focus. This is quite tricky though but there are some good tutorials on panning.