Understanding how to achieve proper exposure is the fundamental key to photography. No one likes a too dark or too bright picture. That is exposure! Read this article and you'll learn how to adjust your camera to get the perfect shot.
In this image, the blur of people moving around in the crowd makes it look interesting, but it is also focusing on particular people who are standing, walking, moving in what looks like a busy area. A slow shutter speed is used in this image.