Role
In books or articles where ghostwriters are being used, the division of work between the ghostwriter and the credited author varies a great deal. In some cases, the ghostwriter is hired to polish and edit a rough draft or a mostly-completed manuscript. In this case, the outline, ideas and much of the language in the finished book or article are those of the credited author.
In other cases, a ghostwriter does most of the writing themselves, using concepts and stories provided by the credited author. In this case, a ghostwriter will do extensive research on the credited author or their subject area of expertise. It is rare for a ghostwriter to prepare a book or article with no input from the credited author; at a minimum, the credited author usually jots down a basic framework of ideas at the outset or provides comments on the ghostwriter's final draft.
For an autobiography, a ghostwriter will interview the credited author, their colleagues, and family members, and find interviews, articles, and video footage about the credited author or their work. For other types of non-fiction books or articles, a ghostwriter will interview the credited author and review previous speeches, articles, and interviews with the credited author, to assimilate their arguments and points of view.
Ghostwriters are hired for numerous reasons. In many cases, celebrities or public figures do not have the time, discipline, or writing skills to write and research a several-hundred page autobiography or "how-to" book. Even if a celebrity or public figure has the writing skills to pen a short article, they may not know how to structure and edit a several-hundred page book so that it is captivating and well-paced. In other cases, publishers use ghostwriters to increase the number of books that can be published each year under the name of well-known, highly marketable authors.