That's called Dock, You can press Option+Command+D at the same time to show/hide the Dock.
Mac OS X window operation shortcuts
Finder section
key combination shortcut
Command-A to select all items in the frontmost Finder window (or desktop contents if no windows are open)
Shift-Command-C Open Computer window www.2cto.com
Option-Command-F Navigate to the search bar in an open Spotlight window
Shift-Command-K Open the Network window
Command-M to minimize window
Option-Command-M minimize all windows
Command-N New Finder Window
Option-Command-T Hide Toolbar/Show Toolbar in Finder Window
Command-W to close the window
Option-Command-W close all windows
Command-` (accent key – above the Tab key on a US English keyboard layout) Cycle through open Finder windows
Control-Command-Up Arrow Open the contained folder in a new window
Applications and other Mac OS X keyboard commands
key combination shortcut
Option-Command-Spacebar to display the Spotlight search results window (may cycle through keyboard layouts and input methods for a language if multilingual is installed)
Control-F4 Focus the active window or the next window
Shift-Control-F4 Focus the previous active window
Control-F7 temporarily overrides the current keyboard control mode in windows and dialogs
F9 collage or uncollage all open windows
F10 Collage or uncollage all open windows in the currently active application
F11 hide or show all open windows
Command-` Activate the next open window in the frontmost application
Shift-Command-` Activate the last open window in the frontmost application
Option-Command-` Focus Window Drawer www.2cto.com
Command-: Show the Spelling window
Command-, opens the preferences window of the frontmost application (provided the application supports this shortcut)
Command-A Highlight all items in a document or window, or highlight all characters in a text field
Shift-Command-C Display the Colors window
Command-F to open the Find window
Command-H hides the currently running application window
Option-Command-H hides all other running application windows
Option-Command-I to display the inspector window
Command-M Minimize active window to Dock
Option-Command-M Minimize all windows of the active application to the Dock
Command-T to display the Fonts window
Command-W to close the frontmost window
Shift-Command-W Close the file and its associated window
Option-Command-W to close all windows without exiting the application