Many sites do not use any fancy Content Managment System (CMS) to generate their pages, they are just just good ol' static HTML content. A site for your grandmothers pie baking business probably only has a few pages, perhaps a homepage, about page, and contact page. Each of these pages has different main content, but much of it stays exactly the same, like the header, navigation, and footer. Think of these sections as "modules" that you can easily use PHP to insert into the page. This way, making changes to those sections changes all the pages at the same time, saving you time and potentially mistakes. At the end of the video, you will see how you can still achieve unique effects in your navigation despite the code being identical. This is great for you Internet CSS website designers out there.