From Diablo Wiki
The story scrolls basically replicate the function of the secret tomes found throughout the dungeons in Diablo I and II, but you need not stand there and watch the text roll up the screen while hearing the narration. Thanks to the improved interface in Diablo III, you can listen to it while you fight, shop, or just stand still, and you can stop, replay, or pause the scrolls at any time.
Only one scroll, Lachdanan's, was present in the BlizzCon 2008 demo, but there will be others in the final game. It's not known if they will require the scrolls to listen to, or if they'll be added to an interface like the Quest window, allowing you to play or replay them whenever you wish.