The hand is in general considered, along with the foot, to be one of the hardest features of the human body to depict in a figure drawing. The reason for this however is usually a lack of knowledge of massing, which is crucial when it comes to drawing human figures.
With so many parts to the hand, many of them moving seemingly independently, massing these separate parts is necessary to any figure sketch you attempt of this area.
This video is from figure drawing instructor Robert Stollar, a self-taught sculptor with a passion for figure drawing. A passion and, of course, a necessity. He lives in Sydney, Australia with his beautiful wife and three dogs, working as a sculptor and teaching figure drawing.
For those who cannot attend his classes in person Robert has an online version of the lectures at Figure Drawing Online.