Mac OS X keyboard shortcuts - Part 1

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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 that has  a  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. A modifier key alters the way other keystrokes or mouse clicks are interpreted by Mac OS X. Modifier keys include: Command, Control, Option, Shift, Caps Lock, and the fn key (if your keyboard has a fn key).

Here are the modifier key symbols you can see in Mac OS X menus:
Command key icon (Command key) - On some Apple keyboards, this key also has an Apple logo (apple
Control key icon (Control key)
Option or Alt key icon (Option key) - "Alt" may also appear on this key
Shift icon (Shift key)
Caps lock icon (Caps Lock) - Toggles Caps Lock on or off
fn (Function key)
Startup keyboard shortcuts
Press the key or key combination until the expected function occurs/appears (for example, hold Option during startup until Startup Manager appears, or Shift until "Safe Boot" appears). Tip: If a startup function doesn't work and you use a third-party keyboard, connect an Apple keyboard and try again.
OptionDisplay all bootable volumes (Startup Manager)
ShiftPerform a Safe Boot (start up in Safe Mode)
CStart from bootable media (DVD, CD, USB thumb drive, and so forth)
TStart in FireWire target disk mode
NStart from NetBoot server
XForce Mac OS X startup (if non-Mac OS X startup volumes are present)
Command-VStart in Verbose Mode
Command-SStart in Single User Mode
See also: Startup key combinations for Intel-based Macs.