The menu structure of most sites is arranged in a 'Tree View' or Hierarchy. Typically, you will click on a menu item (which is just a page). That page will have some content and (possibly) other pages below it. These pages can have pages below them as well, too an unlimited depth.
Here is a simple site Hierarchy:
- Home
- Products
- Product Category 1
- Product Category 2
- Product Category 3
- Services
- Service Type 1
- Service Type 2
- About Us
- Contact Us
To add a new Product Category page (Product Category 4), you would just browse to the Products page and click Add Page. You could also go to Dashboard | Content Manager | Web Manger and browse to the Products page and click the Add Page button.