If you are writing a book, the sooner you learn to actually use styles and other Word features, rather than just click boxes on the Home tab, the better. Spending a couple of hours now will save you days if not weeks of frustration later.

• Basic Concepts of Microsoft Word - from Shauna Kelly (Start here, go through all of the pages in the tutorial, even if you think you don't need it.)
• Importance of Styles in Word (Read the snippet that this takes you to in the lengthy web page. Save the link to the page for later if you need it.)
• Tips for Understanding Styles in Word by Shauna Kelly
• Managing Word Styles by Suzanne Barnhill, MVP

You will recover the time spent reading all of those pages within two weeks of writing using Word. From that point forward, you will be ahead of the game and much more happy with Word.