How to shoot photos with light trails and crystal clear water?

I just have my DSLR camera its Nikon D5100 with 18-55 mm kit lens i'm still learning the curves i already know how to use the Scene and Effect mode but i don't know how to shoot those light trails like mostly taken in the street or highway? Also how to take a picture of moving water to make it crystal clear? How to do it on my camera what mode that i should use.

For light trails you need a long exposure (Tv mode and exposure of a few seconds, or bulb mode and cable release), and for that you'll need a tripod if you haven't got a decent surface to put the camera on.

For clear water which I presume means no reflections, you'll need a polarising filter. You can't magically make moving water clear using photography. You can make it smooth by using a long exposure and for this you may need a neutral density filter to increase the exposure time.

For light trails, you need a long exposure, and that usually means that you also need a tripod to hold the camera steady. You can't hand-hold a camera steady enough tor good light trails, but sometimes it is possible to brace it on something. But for the best results, use a tripod.

Making moving water clear is more of a challenge. Actually, most people want to achieve the opposite effect - making moving water appear like cotton. That can be done by selecting the proper shutter speed. Too short, and the water will appear clear, and too long, and it's just a blur. Usually, a shutter speed of 1/8 or 1/15 second will produce a nice effect.

But to make the water appear totally clear and transparent, you need to do two things. First, you need to avoid any blurring at all, and that means using the fastest shutter speed possible.

The other issue is that water is reflective, and to make it appear totally clear (so that you can clearly see what is UNDER the water), you need to remove the glare caused by surface reflections. You can do that with a polarizing filter.

The challenge, however, is that a polarizing filter absorbs light - anywhere from 1/5 to 3 stops worth. And that means that you need to increase exposure to compensate for the density of the filter. There are two ways to do that - a longer shutter speed will allow more light to pass through the lens onto the light sensor, but that also means that you are likely to get some blur. So the alternative is to use a larger aperture.

But you have the 18-55mm kit lens. Now, that's not a bad lens, but it's not an expecially 'fast' lens - the maximum aperture is 4.5.So if the lens imposes a maximum aperture, and the desire to freeze the motion of the water imposes a minimum shutter speed, then your only remaining option is to allow the camera to shift to a higher ISO setting. Unfortunately, that means that you may loose some resolution (digitheads call this 'noise').