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 a
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:
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.
See All Key for OS X here