Here you will see the Code of your website, you get to this view by clicking Code. Your website is built up with html code.

Hypertext Markup Language is the authoring software language used on the Internet's World Wide Web. HTML is used for creating World Wide Web pages.

Here you will see both settings, design view and coding view, you get to view this by clicking Split.

This is helpfull because if you highlight something in your design it will show you the html used. A good way to find mistakes and errors.