The Taskbar
This is the default bar on your desktop that has the Windows Start button on it. Buttons which represent programs, documents or windows appear on this bar when you open that program/document/window e.g. the button with the text 'Sage Control Centre' in the above screen-shot represents the Sage Control Centre Help file. You can use these buttons to quickly switch between the open windows. The button of the currently active application looks like it is pressed in.
If the taskbar is set to Auto hide it is only visible when you move the mouse cursor over the area where it is normally displayed, or when you press Ctrl + Escape. It is effectively hidden from view until you do one of these things. You can turn Auto hide on and off by accessing the Taskbar's pop-up menu and selecting Properties (click the menu mouse button on a blank space on the taskbar). Tick the Auto hide tickbox to turn it on.