Use keyboard function keys on Mac
The top row of keys on an Apple keyboard are called function keys. Function keys can be used to perform keyboard shortcuts or to control system features, as indicated by an icon on the key. For example, you can use F11 as a keyboard shortcut to show the desktop or to decrease your computer’s volume.
By default, keyboard function keys are set up to control system features. To use the function keys for keyboard shortcuts, you must also press and hold the Fn key or the Globe key 
(depending on your Mac model or if you’re using a Magic Keyboard). For example, to show the desktop you must press Fn-F11 or -F11.
If you use the keyboard function keys for keyboard shortcuts more often than for system features, you can set an option so that you don’t have to press and hold Fn or .
On your Mac, choose Apple menu
in the sidebar. (You may need to scroll down.)Click Keyboard Shortcuts on the right, then click Function Keys in the list on the left.
Turn on “Use F1, F2, etc. keys as standard function keys” or “Use F1, F2, etc. keys as standard function keys on external keyboards” (depending on your Mac model).
