People who learned to write using pen and paper often have difficulty appreciating that a word processing program "thinks" differently than a person. A person starts with a sheet of paper and adds things to it. A word processor wants the user to actively define the page (margins, headers, and footers,) then define paragraphs using styles. For a simple document that's a fair bit of work, although most word processors today have default templates that will set up a decent set of styles for you.
Styles are powerful: you can easily change the look of an entire document by changing the base style to use a different font, line-height, or margins. Or change the layout from block paragraphs with an empty line between them to indented paragraphs with no empty line. But unless they've specifically learned that, either by reading the manual (yikes!) or taking a course, they won't even know that functionality exists.
I'm unsure how many of these concepts are covered in school today. That seems to be the place to introduce these, starting with 12 to 14 year old students.
Much of the above applies to web pages, too: HTML contains the content while CSS tells the browser how to present that content. And don't get me started on how horribly mangled is the HTML generated by both MS Word and LibreOffice Writer.