A handbook is a guide or list of instructions on one particular subject. A new car comes with a handbook explaining how its controls work and giving tips for problems that arise. Sometimes new parents wish their newborn infant came with a handbook.
A handbook is a type of reference book, offering information about a topic or a machine. Your bird handbook might include pictures of birds in your region, and the handbook that came with your blender will tell you how to use it and also might include several smoothie recipes. In Old English, it was handboc, though in Middle English this was replaced by manual, thought at the time to be a much prettier word.