Photoshop - Levels

In photoshop, to create different levels of tonal imagery you can use tools to adjust the lighting of the photo and to change the contrast and the tonal levels.
This tool is helpful to bring out colours and make the image more effective and impressionable. It can also be used to eradicate imperfections.

This image I have found on the interent will hopefully demonstrate this:

 

As you can tell, the colour have been brightened, and the tones in the creases if the rocks have become darker. Various other tools have been used, such as the perspective tools, but focusing on the levels of this image, you can tell it has rappadly changed.