about audio book

what is audio book in sansa clip(2 gb)?

Are you just trying to figure out what an Audiobook is? Or are you trying to add one?

i want to know what is audio book.and how to add it

Audiobooks are like the digital versions of books on tape. How you add them is up to you. If you choose to use audible, then thats like one stop shopping. There are dozens of other ways incudling windows media player that you can use.