The story of Hanukkah is that is was a very dark time in the life of the Hebrews.  There was a tyrant on the throne, Antiochus Epiphanies, who treated them poorly.  They were basically slaves, and he desecrated their temple.  A leader by the name of Judas Maccabeus led a revolt called the Maccabean Revolt.  They attempted to restore the temple again.  The holiday of Hannukah celebrates the restoration of the temple as a place of hope during the dark time, and the miracle of the oil keeping the lamps lit for 8 nights, even though they only had enough oil for one night.  That is why 8 candles are lit during Hannukah.