Fusion is an application which will help you create an image with a high-dynamic range of brightness, popularly known as an HDR image. HDR images have more shades of light than normal images, since you have the overexposed as well as the underexposed image. The HDR image has more colours than an ordinary photograph.
To use this application, you will need photographs that have different exposures. The subsequent tone mapping to low range uses non-linear algorithms which allow you to preserve the maximum details of the original photographs.