The single special mitzvah for Chanukah is to light the candles which commemorates the miracle of Chanukah.

The purpose of the Chanukah candles is pirsuma nisa – to publicize the miracle of Chanukah. Therefore, the Rambam writes that the Chanukah candles should be lit at shki’ah (sunset), but that we may continue to light until the people come home from work. (Hilchot Chanukah 4:5; Shulchan Aruch 670:1-2)