How much does he know about the story before he begins? For instance, does he know the end of the story in advance?

Once he's decided on the theme, he starts to mentally outline the story and begin running through possible ideas. Before he starts writing, he knows how the story begins and ends, as well as five or six of the major events in the novel, which serve as turning points. Once he has those things, he's ready to begin. Most of what happens in between the five or six major events is created as he proceeds.