Sometimes you don’t want headers and footers to look exactly alike on every page of your document.
For example, you can get a clean looking first page by leaving the header off. Or, if your pages are printed on both sides of the paper, the convention is to place page numbers so they’re always on the outside margin, alternating position on odd and even pages.
This video will be easier to follow if you already know how to add headers and footers to your document. To learn how, see Video: Add a header or footer to your document.