Look at the above two images. How do you find them? Note that first image was taken with flash ON while the second one was taken with flash OFF.
I'm sure some of you are confused. If first image was taken with flash on, why is it darker than the second one???
The reason is simple. The little flash wasn't powerful enough to illuminate the skyscraper.
But why is the second image brighter? To answer this question, we need to understand the concept of exposure. When we press the shutter button, the lens is 'opened' for certain length of time, allowing light to enter the camera and expose the image sensor (or film). The longer the exposure time, the brighter the final image will be, and vice versa. (Assuming that other factors are held constant.) In a camera, exposure time is determined by shutter speed.
I switched off the flash when I took the second image. The camera automatically selected a slow shutter speed of 1/6 sec, which means the exposure time was 1/6 sec. In contrast, the first image was shot with a shutter speed of 1/60 seconds.
When taking a night landscape picture, turning off the flash will 'normally' force the camera to select a slow shutter speed, and you get a better photo. (There are exceptions, but we will not discuss them here.)
Alternatively, use Landscape Mode or Night Landscape Mode, if your camera has one.
When you are shooting with slow shutter speed, the camera should be stabilized using tripod.