In the world of art, there are more ways to create a drawing or painting than just using a few colors. First, there are shades of color to use. You may want to use dark blue, light blue as well as the shades in between those hues. Likewise, there are degrees of lightness and darkness in the colors and shades of different colors. There are different shades of lightness and darkness to simple black and white drawings.
The term used to describe this lightness and darkness is called value. While drawing an apple, there is a source of light that will shine onto the apple which may cause a shadow underneath the apple if the apple is sitting on a table. This is where value shows in a drawing.