Start Button

Click this to open the Start Screen (which is the replacement for the Start Menu in Windows 8)

Pinned Programs

Known as the Quick Launch Toolbar in Windows XP and Vista, you can pin shortcuts to your favorite programs here so you can launch them quickly

Open Applications

All currently opened applications/windows are shown here so you can easily switch between them

Notification Area

Shows date/time as well as system icons for network connections, power, audio volume, battery level (if laptop/tablet), Action Center messages etc as well as notifications for background applications such as your virus/firewall software

Thumbnail Preview

Hover over any minimized or pinned programs on your taskbar to get a thumbnail preview of that window, makes it easier to switch between applications and choose the windows you want active