Christmas Day (celebrated on December 25th, the exact date is unknown) is an important day for Christians, when they celebrate the birth of Jesus. It is marked by the giving and receiving of presents and remembers the gifts given by the wise men – see Epiphany.
Advent is the four week period leading up to this time, a time of preparation, and it’s progress is noted in some churches by the lighting of special candles, usually in an Advent crown, on each of the four Sundays before the day.