As you can soon discover, there’s not a classic desktop like the previous GNOME releases (or MS Windows and Apple OS X), no files can be saved on the desktop, neither it reacts to right clicks. This is the default behavior but can be modified to restore the classic desktop with icons in the background behind the windows. We’ll see later how to control the desktop behavior.
The top panel will show on the left corner the Activities button from which you can see all your open windows and workspaces, launch new applications and make a search for resources or general terms using an on-line search engine.
On the center of the top panel you can see the Clock menu so that when you click it the calendar will pop, showing your appointments from the Evolution organizer.
On the rightmost part of the top panel there will be the the User menu showing your on-line status (for the IM application Empathy) and your full name. On its left lies the Volume and the a11y (Assistive technologies) menus in the so called System status area.
To the right of the Activities button finds its place the Application menu which only function is to allow to quit the application.
It will only appear when a window is visible in the foreground and the menu will hide itself when there are no more windows visible in the foreground.
If you move the mouse pointer in the right down corner of the screen a black faded bar will appear, with no content at all. Such bar is called the Notification and message tray and offers place for applications to communicate with the user using messages.
When some application sends a notification to the user the message tray will appear for some seconds and it will automatically hide if the user doesn’t move the mouse upon. Some messages are not important (like songs title from the audio player) and they will not be keep after the automatic hiding. Some other messages are considered important and they will be preserved until the user reads them by opening the message tray.
The old notification tray for some running but hidden applications is now integrated in the right side of the notification bar. While the usage of the such bar is discouraged a lot of applications still rely on this area so it was still preserved. The notification icons can react to user clicks for both left and right buttons but this depends from the application.
Further information can be found in: GNOME Shell Design.