Writing a book.

Adobe InDesign is a good program, especially if your book is going to incorporate graphics/illustrations along with text. It's a desktop publishing program. It's not cheap but if you know where to look, you can find past versions to download for reduced prices. Or, the older versions don't have the same licensing restrictions so you can buy used copies for cheaper than new. I would link you to the site where I downloaded my copy but I can't find it now . It's a good investment if you are serious about producing this book as well as more in the future.