All of the documents, images, and pages of your site are stored in Libraries; a fancy name for a folder. As you add more content to your site you will want to know where these libraries are stored and how to manage them.
Site Structure
Every SharePoint site starts off as a basic site with a few pages. As the site grows, you can add more sections to your site to help you group your content. These new sections are called Subsites.
Each subsite gets its own set of folders. You can also control the navigation links under each subsite.
Here's an example of a site structure with a few subsites: