The header and footer are static, meaning that the header and footer will remain the exact same across every page. In comparison, the body content of every page is different. What that means is if you edit the footer on one page of your mobile website, it will make that change across all your other pages as well.
This makes it a great place to insert things you want to appear everywhere on your site. From logos to copyright information, simply add the content you want into the header/footer to get it to appear on every page in your mobile site.