A higher ISO will enable you to use a faster shutter speed in dark conditions giving you much sharper image. But the higher ISO will also result in more noise produced in the photo. I would only recommend a low ISO + long exposure when shooting at night, if the camera isn't being pointed at a direct light source, otherwise any street lamp, or headlight for example will result in large starring.
I would recommend a slowflash and ISO of 400-600 for photographing cars at night.
As for aperture and shutter speed settings, it will totally depend on the lighting conditions, and the way you want to compose the shot.
Aperture will effect the amount of light that can enter the lens, and can also be used to adjust the depth of field of a photo. The lower the aperture, the more light will pass through the lens. The higher the aperture, the less light will pass through. This is why lens with a fixed aperture of f/2.8 are so expensive, because they allow you to use a fast shutter speed in low light situations without using a high ISO. Aperture also depends on focal length. To make it as simple as possible, the more you zoom in, the higher the minimum aperture will become. Your lens will have two minimum apertures. One for at the lowest focal length and one for at the highest. For example my lens is F/3.5-5.6. Meaning at 18mm the lowest aperture i can set is f3.5, and at 55mm the lowest is f5.6.
As for depth of field, using a small aperture (f3.5) will produce photos where anything behind the subject is out of focus, a large aperture (f22) will make the foreground and background both in focus.
Once you have the correct aperture, choose the shutter speed to match. You could probably guess by the name, but shutter speed is the option of how long the shutter stays open for. Most DSLR's have a shutter speed bar on the display, to tell you how under or overexposed the photo is going to be. Although this is useful it doesn't always work very well, because it depends if theres a bright light visible (tricks the camera into thinking a faster shutter speed is needed).
Fast shutter speeds will freeze the action/motion in a photo, where as a long shutter speed will give the impression of motion (like the light trials/blurring in the photos posted in this thread).
If using a dslr or high end compact, you will have aperture and shutter priority modes. Start off using these before using fully manual. It will give you an understanding of how they work in the real world.
Aperture mode, means the camera will automatically adjust the shutter speed.
Shutter priority mode means the camera will automatically adjust the aperture.
I hope this helps some people!
