I want to sketch with graphite pencils but am confused about the range of options. What do the pencil grades mean and how can they be used?

Graphite pencils come in a range of grades — from hard (9H to H) to soft (HB to 9B). A hard graphite pencil leaves less graphite on the drawing surface and can be used to produce faint, sharp lines and build texture. HB or B pencils are good options for hatching and cross-hatching line work. They don’t smudge as easily as the softer, darker graphite pencils — and create clear lines. Soft graphite pencils are excellent for building solid tones of dark gray to near black.