By default, GNOME usually contains two panels (one on the top, and one to its opposite on the bottom) spanning the width of the screen.
The top panel usually contains navigation menus labeled "Applications", "Places", and "System", in that order. These menus hold links to common applications, areas of the file system, and system preferences and administration utilities, respectively. The top panel usually contains a clock/calendar and a notification area, which can double as a sort of dock, as well.
The bottom panel is commonly empty by default (other than a set of buttons to navigate between desktops and a button to minimize all windows and show the desktop) due to its use in the navigation between windows (windows minimize to the bottom panel by default).
These panels can be populated with other completely customizable menus and buttons, including new menus, search boxes, and icons, with the icons in particular (called launchers) performing functions similar the quick-launch feature found in the Microsoft Windows taskbar.
Other applications can also be attached to the panels, and the panels are highly reconfigurable: anything on these panels can be moved, removed, or configured in other ways. For example, a migrating Microsoft Windows user might move the menus usually posed in the top panel into a 'start' menu on the bottom panel as well as moving the notification area into the place normally posed by the Windows notification area, then remove the top panel altogether, to interact with GNOME panel similarly to the MS taskbar.