One thing to understand about Microsoft Word is that if you want to become proficient with it, you must learn about how to use styles.
Styles underpin everything in Word and you can't do a single thing without using them. Given they're responsible for how your document looks, behaves, and reacts, they're critical.
If you want to know more about them and their importance, I've written some blog posts on the subject:
Quite simply, master styles and you master Word.