Traditionally there are 12 days of Christmas beginning on Christmas Day (December 25) and ending on Epiphany Day (Little Christmas/Three Kings or Wise Men Day) on January 6. Customs vary by country but almost always there are special activities, foods, and in opening of presents as well.
The celebration of Twelfth Night came about in medieval and Tudor England when Candlemas originally ended the Christmas season. A special cake was prepared with a bean and pea hidden inside. The man who found the pea in his slice of cake became king for the night while the woman who found a pea became Queen for the night. Christmas carols and feasting would also take place. A special punch for Christmas, wassail, was often drunk on that night but also during the entire season as well.
Since Twelfth Night is about the impending arrival of the Three Kings, the statues of them would appear in the crib or the following day in countries such as Ireland. Christmas decorations would start to be taken down as well and certainly by the end of Epiphany Day. Edible portions of wreaths (fruits or nuts) would be consumed as part of a feast as well. The famous Shakespeare play Twelfth Night was written as entertainment for the holiday.
Twelfth Night is considered secular by Christian denominations and not a required day of observance. The following day, Epiphany Day, is a solemnity and observed by attendance in church.