Slowing down your shutter speed can help with capturing your motion blur. Letting your cameras shutter open for a long period of time helps. Having a fast shutter speed is not going to capture much movement. Determining your shutter speed can also depend on the speed of your subject. The slower your subject, the slower the shutter speed needs to be to create a blur.
When considering shutter is how much light exists in a scene. The longer the shutter speed the more light that gets into your camera. The more light that gets into your camera the more risks you get of blowing out or overexposing your image. Two ways of getting motion in your in your images could be by having your object move or having your camera move. Using a small aperture and narrowing it can help with less light hitting the camera sensor.