My guess is that this is what it means: Most word processor users do not use styles. They manually change the font, font size, indentation, etc. of each chapter title. They manually press enter a bunch of times to put a big space between the top of a page and each chapter title, or to force a line of text to appear on the next page. They manually fiddle with other presentation details like indentation (e.g. by pressing tab at the beginning of each paragraph) to make the document look how they want it to look. Using styles is a different way to tell the software what you want it to do. You tell the software "this line is a title", "this word is emphasized", "this paragraph is a quotation", etc. In a place separate from the content, you tell the software how to present those things. "put titles in this font, make them this size, put this amount of space above them, and put them on a new page", "make emphasized words italic", "block-indent quotation paragraphs by .5 inches", etc. Using styles is better for many reasons: You do not repeat yourself. That way, if you change your mind about how you want chapter titles to look, then you do not need to go through the document and change each one individually. You just change the style and the document is automatically updated. You separate concerns. That way, you can pretty much set formatting aside, forget about it, and get back to writing. It has semantic meaning. That way, the document carries the information that actually matters. "15 line breaks followed by a line in 18 pt bold Georgia" means nothing. "chapter title" means something. "styling for typesetting" must mean the editor will replace the author's manual formatting with styles, or at least help the author do so. It is really a very menial task that anyone can do after reading a tutorial or two.
