The Apple Menu

The most important Menu Bar in Mac OS X is the Apple Menu, it's located on the far left and can be easily identified by a Blue Apple icon.

You can use the Apple Menu from any application because the Apple Menu never moves of goes away. It is always located in the upper left corner of the Mac OS X screen. The following examples show the location remains despite using a different application:

As with any menu, just select the Apple menu to view a listing of available items. Some of the most importantare:

About this Mac - Lists information about the installed OS version, memory and processor
Software Update - Brings up the OS X software update application to check if any updates are available for your Mac
System Preferences - Takes you to a special system configuration and settings window
Dock - allows you to customize the Dock
Recent Items - Lists the applications and documents that were recently opened or used. The number of items listed can be configured in System Preferences. Launch System Preferences, click Appearance, and then adjust the area called Number of Recent Items as needed.
Force Quit - Bring up a window to allow you to forcefully quit an application (ideally used for unresponsive applications)
Sleep, Restart, Shutdown - Self explanatory
Log Out - Shuts down all running programs and documents (you'll be asked to save any unsaved items) and returns you to the Mac OS X login screen.