Graphite pencils come in various levels of hardness. The graphite within the pencil is processed to have different degrees of hardness or firmness. Some pencils are made of firmer or harder graphite, creating lighter lines and shading. Some pencils are made of softer material, creating darker lines and shading.
As an artist or designer, we can select the correct type of pencil for the task at hand. For example, when we start a sketch, we might use a pencil with firmer graphite to draw the light lines of the initial setup of the sketch. After we work out the light lines of the initial sketch, we might want to shade the drawing using a pencil with softer graphite.