Keyboard shortcuts invoke functions when a user presses a key in combination with one of the Mac OS X Keyboard Shortcuts – Modifier Keys, on their keyboard.
To use a keyboard shortcut, or key combination, you press a modifier key with a character key. For example, pressing the Command key (the key with 
symbol) and the “c” key at the same time copies whatever is currently selected (text, graphics, and so forth) into the Clipboard. This is also known as the Command-C key combination (or keyboard shortcut).
A modifier key is a part of many key combinations. Modifier keys alters the way other keystrokes or mouse clicks are interpreted by the computer. The Mac Modifier keys are: Command, Control, Option, Shift, Caps Lock, and (on portable Macs) the fn key.
Here are the modifier key symbols you can see in Mac OS X menus:
(Command key) – Sometimes called “Apple key”; on Apple keyboards this key also has an Apple logo (
).
(Control key).
(Option key) – “Alt” may also appear on this key.
(Shift key).
(Caps Lock) – Toggles Caps Lock on or off.
fn (Function key) – Located in the lower left corner of built-in keyboards on portable Macs.
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