The main custom on the holiday of Chanukah is the lighting of the menorah, to recall the miracle of the lights. This is primarily sourced in the Talmud (Shabbat 21b):
What is Hanukkah? The Sages taught: On the twenty-fifth of Kislev, the days of Hanukkah are eight. One may not eulogize on them and one may not fast on them. When the Greeks entered the Sanctuary, they defiled all the oils that were in the Sanctuary. And when the Hasmonean monarchy overcame them and emerged victorious over them, they searched and found only one cruse of oil that was placed with the seal of the High Priest. And there was sufficient oil there to light the candelabrum for only one day. A miracle occurred and they lit the candelabrum f… Read More »