The section break allows completely different headers and footers.
Long documents frequently require different headers and footers in different parts of the document. For instance, you need to change chapter headings in a book; you don't want chapters 2 through 15 to say "Chapter 1." Different headers and footers in different sections not only look good, they also allow a reader to navigate a document more easily.
To set up different headers and footers, the first thing is to divide the document into sections. Sections are distinct portions of a document that contain a unique set of formatting attributes (they are not just used for headers and footers).
To create sections, you must insert section breaks between the various parts of the document. You'd do this from the Insert menu (Break command). You'll get a chance to try this out in the practice session.
If you divide your document into sections and you have already set odd and even pages to be different, remember the odd and even pages apply across the whole document. So each of your sections will have odd and even page headers and footers set up. If you don't want this, you'll need to adjust the odd and even settings in each separate section.
If you would like to know more about section breaks, see Word Help.