what it basically does it when ever your car is turned on, they will turn on. when the headlights are on, they will turnoff.
if you leave headlights on, and turn car off, the coil is turned off, so you dont flatten your battery,
if you want to change to using a separate switch, just add a switch between the ignition, and where it branches off.
to see how it works see here.

and here is a drawing that will put it in more prospective for you.

Hmm to me they are sideways, but in photobucket they are the right way,
anyway if you need help explaining it. let me know.
but its seems if you want it to work like that you will need 2 relays, unless the headlight switch has a N/C contact on it, if it does, then that can be used instead of a relay.