Drawing the hands is one of the most difficult challenges faced by an artist when studying anatomy. They are as complex as the rest of the figure. Good reference material can help to simplify the task. Thankfully, the classic fully illustrated text of George B. Bridgman's Book of a Hundred Hands is available free from Google Books. You can download a PDF, read it from your browser or view the book on any device that supports the Google Books app.
Bridgman details the hand in most imaginable positions, detailing fingers, the wrist. Most sections include simplified muscle groups with labels. Other details of interest are the veins, bones and, of course, short texts. The text quickly tells you information that's key to an artistic understanding of anatomy.
If you insist on print, you can also buy the published edition book on Amazon for under $20USD . If you have any other resources, share them in the comments