I'm not sure which key combinations specifically you're referring to. How would I use the old function keys to switch music playing from iTunes to a paused YouT

I'm not sure which key combinations specifically you're referring to. How would I use the old function keys to switch music playing from iTunes to a paused YouTube tab in a Safari window on another desktop? And how would I use the function keys to scrub through a song to find a specific part all without giving focus to the music playing app? Maybe all this was possible before but I never knew about any of it. If that's the case that's another strength of the touch bar -- I had no issue discovering this functionality this time.