When I press the Function keys (F1-F19) nothing happens. How do I use the Function keys?
By default, Mac OS X uses the F keys to control items such as volume and brightness. To use an F key for a game command hold down the fn key, then press the F key you wish to use.
To automatically enable the F keys, follow these steps:
Open System Preferences ( Menu → System Preferences).
Click on Keyboard or Keyboard and Mouse (depending on the version of Mac OS X you are running).
Select the Keyboard tab.
Check the Use F1, F2, etc. keys as standard function keys checkbox.
The F keys will now work without using the fn key.