GNOME Shell Activities/Overview
Taskbar + Start Menu = Activities/Overview
The whole Activities/Overview change has been a source of puzzlement to many of the folks who followed the early development of GNOME 3. The best way we can describe the Overview to a Windows-oriented audience is: taskbar and Start menu in one. Imagine if the Windows taskbar lacked a task/window list, but simply hosted the notification area and the Start button. The list of open applications and windows would then be located within the Start menu.
The Activities button in GNOME 3 replaces GNOME 2's Applications/Places/System menu. Instead of a menu, the Activities Overview is a full-screen overlay housing various OS controls. The Activities Overview is separated into five main areas: Dash, Windows, Applications, Search, and Workspaces. The Messaging Tray is also locked in place in the Overview.
Like Ubuntu's Unity, GNOME Shell also has an element known as Dash. Unlike Unity, where Dash is essentially the Start menu, GNOME 3's Dash is an off-screen dock. Favorite applications can be pinned to the Dash where their icons serve as quick-launchers.
The icons of open applications also appear in the Dash. A subtle spotlight effect underneath the icons of open applications differentiates them from pinned quick-launchers.
When the Overview is activated, the bulk of the screen displays the Windows view by default. The Windows area of the Overview presents all of the currently-open windows in a way that's very similar to the Compiz plug-in, known as window spread.
In Windows mode, the user can switch to other windows, close windows, and move them to other workspaces (explained later).
Near the top of the Overview, next to Windows, is Applications. Selecting Applications changes the bulk of the screen from Windows view to Applications view.
The Applications view lists all of the installed applications as large icons. The listing is in alphabetical order, though a right-side pane holds traditional application categories. Selecting a category narrows down the full list, only displaying applications from the selected category.
While there are text labels below each application icon, the size of the text is comically small when juxtaposed against the oversized icons. The font used wouldn't have been our first choice, either. Between the diminutive writing and font, the labels are sure to cause more eye strain than their existence is worth.
The Overview also features a search box in the upper right-hand corner. Semantic search results are provided by Zeitgeist. Typing characters into the box instantaneously populates the Overview with relevant applications and files. The Wikipedia and Google buttons near the bottom of the screen open a Firefox window with the corresponding search results page for the term entered.
GNOME 3 employs the same workspace metaphor as MeeGo (previously known as Moblin, now Tizen). Instead of a predefined number of virtual desktops, GNOME 3 spawns new workspaces as needed.
The way this works is pretty simple. There is one more empty workspace than the number of workspaces currently in use at all times. Moving any window to the extra desktop spawns a new empty workspace. Thus, you can never run out of workspaces. The on-screen representations simply get smaller and smaller in order to fit more workspaces in the Overview.
If that still seems confusing, the video below is more illustrative.