The roles played by each of the function buttons can be selected by pressing and holding the button. The default options are shown below:
Fn1 button (Photometry)
Fn2 button (Control ring options)
Fn3 button (Film simulation)
Fn4 button (White balance)
Fn5 button (AF mode)
AEL/AFL button (Exposure/Focus lock)
Center of rear command dial (Focus check)