Graphic design is not a single skill or application. It has a variety of stages with varying levels of importance determined by what the project application most calls for. It could as simple as a multitude of low quality sketches to aid in a planning processes or to help with setting a point or idea, or as complex as a single intricate work of art that inspires awe upon all those who behold it, or anywhere in between.
Sketches are the base of which all artwork begins. The foundation that directs the development process and guides the idea that is to be portrayed.
Detailing provides form and structure to artwork. At this point the image is more refined and presentable.
Colour provides a sense of life to any art piece. allowing for a far greater level of expression.
Shading helps ground the artwork in realism by providing a sense of depth and texture.