You can find document parts, or building blocks as we'll call them, in galleries. And you can find galleries filled with headers and footers, watermarks, tables of contents, cover pages, and even boilerplate text, throughout the tabs on the Ribbon. Each gallery contains many built-in designs. For example, if you want to add a cover page to your document, open the cover page gallery and choose a design that works for that business plan you're creating.
Built-in designs save you time because you just choose a design, replace the placeholder text with your own, and you're done.