Here's a screen shot -- I'm editing the site structure for this site. In the background is my outline of Manila sites. Note that the Current node in the discussion group is expanded. You can read dg messages in-line. There are commands for replying to a message and creating a new message.
Yes, you got it right -- I'm editing the site structure, but the XML is hidden.
Also note icons for Home Page, Navigation, Template, etc. To edit any of these, you double-click.
Not shown is another feature: when you edit a page, that page is added to the sub-outline for that site, so you can get back to it later.
Also: you can bookmark your home page, other pages, and templates.