The most useful Function key on a Macbook keyboard is F3 …to jump between multiple screens or windows.
However, when you plug in an external keyboard to a Macbook Pro or Macbook Air and use a non-apple keyboard, then the function keys do not behave as they did on the Macbook itself.
F3 key does not work as it did on the Macbook (Dell keyboard , F3 is audio increase)
The F3 on Macbook is actually “Mission Control” and same functionality can be achieved by hitting “control” (or ^) plus the “up-arrow” key.
This may differ from Osx versions but can be confirmed by going to “System” > “Keyboard Shortcuts” > “Mission Control” to see what shortcut is assigned to “Mission Control” and the other Function keys