When you open the header and footer workspace, the newly created sections are indicated.
The section break means that what comes before it is one section, and what's after it is another section. So, with the section break inserted before chapter 1, all the front matter — the cover page, table of contents, list of illustrations, and so on — becomes section 1, and all the chapters become section 2. (This assumes that all pages and chapters are in one document.)
When you open the header and footer workspace, markers appear there that define the sections and keep you oriented. As the picture shows, the header and footer areas indicate the sections and give each a number.
This footer is at the end of section 1.
The header below is at the start of section 2.
And you'll notice another tab: Same as Previous
. What does it mean?
It means that, though you've created distinct sections in the document, Word still gives you the option of having header and footer content carry over between sections. In the illustration, the Same as Previous tab on the header's dotted line means that header content for the new section is linked to header content in the preceding section. If you want the headers in the new section to be unique, you have to break the link to the earlier section.
The same will be true for all the footers in the new section. They'll carry over footer content from the previous section unless you break the link in the footer.