Hilchos Chanukah - Laws of Chanukah
On the first night light one candle on the right side of the Menorah as you face it. On the second night, add one more candle to the left of the first one. Make the Brocha and light the newest candle first and then move towards the right lighting the other candles. Each night add one more candle to the left and light the newest one. It is this newest candle that speaks to the Chanukah miracle because with each new night, the miracle became greater.
--Shulchan Aruch 676:5