The article about function of the F1-F15 keys using Fn appears to be inaccurate for El Capitan.
I go to System Preferences / Keyboard as the Apple support article suggests, but there is no setting for using the Fn key.
There WAS an option there in previous OS X versions. Did this get moved somewhere else?
iMac (27-inch Mid 2010), OS X El Capitan (10.11.3)