Hanukkah is an 8-day Jewish festival that commemorates the rededication of the Second Temple in Jerusalem. It involves lighting candles on a menorah each night, eating foods like latkes and jelly doughnuts, playing dreidel games, giving gifts, and celebrating miracles in Jewish history like oil lasting for 8 days after the Greeks desecrated the temple. The main celebrations include lighting candles, saying prayers, singing songs, eating food, and playing the dreidel game, with an additional candle lit each night for the full 8 nights.