So what are styles? You have heading styles. This would include things like the title of the book, the chapter headings or story sections. Then you have body style which alows you to set the paragraphs of a novel or story. You can set your quote styles and more. As a writer submitting short content to magazines, you could set up styles based on the submission requirments.
To start learning how to set your own styles, you can do a Google search "How to use Styles?" Or some such. However, from my personal experience, I had to have an pretty good understanding on formatting at the paragraph level before Styles and the tutorials made sense.