Aside from the Start screen, the Charms bar is probably the second-most important part of the Windows 8 UI. It contains Windows 8's version of the Start button, along with four other functions that change depending on the current app (or the main app, if Snap is being used).
The Charms bar is activated by moving the mouse cursor to either the top- or bottom-right corners of the screen. When the cursor hits one of these hot corners, five white icons appear from the right side. From there, move the cursor toward the center Windows icon. A black bar now appears that makes the Charms bar active.
You'll find five tools (or charms) on the bar. From top to bottom, you have Search, Share, Start, Devices, and Settings.
The Search charm defaults to the Apps filter when activated from the Start screen or desktop, but you can switch to the Settings or Files filter (or to any of the Windows 8 apps currently installed on the system).
If the application you wish to search isn't already open, it launches in the main Snap area, leaving the Search charm active as a sidebar on the right side of the screen.
The Share charm gives you different ways to share content inside of an app. For instance, the Toshiba Satellites came with the StumbleUpon app pre-installed, and Windows 8 comes with Mail and People apps. So, on those systems, I have three ways to share content from another piece of software like Internet Explorer 10.
When a share is started, the app creating it becomes a double-wide sidebar on the right-hand side of the screen.
This charm is simply the Start button for the Windows 8 UI; selecting it opens the Start screen.
The Devices charm gives applications access to connected devices like monitors, projectors, and printers. You would use the Devices charm to print a webpage, for example, or to connect your laptop to a projector or HDTV.
The top portion of the Settings charm contains options for and information about the current app.
The bottom portion provides quick access to essential PC functions, such as a networking manager, volume and brightness sliders, notifications, sleep/shut down/restart, an on-screen keyboard, and PC settings (the Windows 8 UI equivalent of the old Control Panel).
Whenever the Charms bar is invoked, an opaque black box also appears in the lower-right corner of the screen. This area contains indicators for things like the network connection, battery, time, and date.
So, with the Start button, devices, clock, and indicators, the Charms bar operates a lot like the taskbar in Microsoft's Windows 8 UI. Well, half of the taskbar, anyway. We're still missing the equivalent of a window list (where all of the currently-open windows can be selected). That functionality is handled by the bar on the left side of the screen, called the Switcher.