How to automatically add “read more” button

[Naki]

I am trying to develop one html page for reading stories. Now for longer stories (length>VALUE), I want to have a "read more...." or "continue reading" button appearing automatically for those stories.I tried googling for it, but all i found was for blogger account, But the page which i am trying to create is not blogging type.FYI: I am not having any custom framework involved here such as Zoomla, wordpress etc;It is just aq simple html page having JS and CSS integration.Kindly helpNote: The story which I am getting is being fetched from database dynamically