It's part memoior and part exposition. King talks about the rules of writing, and the craft of becoming a good writer. He also discusses his personal journey as a writer. He discusses how he developed certain writing/working habits, his highs and lows as a professional writer, and his choice of genre. It's a great mix of personal story and sound advice.
King talks about the process of writing openly and honestly. To him, writing is an honest profession. A real writer writes for himself, and writes all at once with no interruptions. A real writer writes clearly and plainly, with little frill, and writes first and edits later. Writing is about baring your soul, but it is also about putting words to paper.