The function keys on your Magic Keyboard provide shortcuts for common functions, such as increasing the volume or screen brightness.
Mission Control key (F3): Press to play or pause, or to increase or decrease the volume of sound from the built-in speakers or 3.5 mm headphone jack.
Function (Fn) key: Each function key (on the top row) can also perform other functions—for example, the F11 key can hide all open windows and show the desktop. Hold down the Fn key while you press a function key to trigger the action associated with the key.
Tip: Press the Fn key twice to turn on dictation, which lets you dictate text wherever you can type it (for example, in Messages, Mail, Pages, and many other apps).
Set keyboard preferences. Use the Keyboard pane of System Preferences (choose Apple menu Keyboard shortcuts on your Mac.