Here are the modifier key symbols you can see in Mac OS X menus:

(Command key) – On some 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)

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.