Even though night has fallen on Saturday night, Shabbat does not leave us until we usher it out through havdalah. Thus, if you need to drive, light the fire, or do any other act forbidden on Shabbat, once Shabbat has ended, make sure to say a mini-havdalah: Baruch hamavdil bein kodesh lechol, “Blessed is He who separates between holy and profane.” You can then go about your business.