The major religion in the Czech Republic is Christianity so Christmas is also the major winter holiday.
I picked eight of the most interesting Czech Christmas facts and traditions:

1) Czechs open their Christmas gifts right after the dinner on December 24th
2) The traditional food is a fried carp (fresh water fish) and potato salad. Families usually go buy a live carp and let it live in their bathtub for about a week, then on Christmas day, the father of a family kills the carp and gets it ready to cook. Usually the entire family (mother+father+kids) help to cook. I am really looking forward to the carp-killing part of my fatherhood!
3) It is baby Jesus and his little angel helpers who bring gifts to children, NOT Santa!
4) The Christmas tree is usually put up and decorated a day before December 24 and left up until mid January.
5) Christmas tree decorations include a lot of chocolate and other candies so the glory of the decorated Christmas tree diminishes significantly with the progress of holidays.
6) Baking Christmas sweets and cookie-like things is one of the most important tasks in a life of a Czech grandma.
7) Czechs get the December 24, 25, and 26th off work. Either the 25th or 26th are almost always spent with the entire greater family.
8) The Czech Republic usually has snow from early December to mid-March so skiing, sledging, and snow-balling are among the most popular activities during this time.
The first following link describes some interesting Czech traditions and other information, the second link includes some traditional songs and more.
www.czechtourism.com/eng/uk/docs/holiday-tips/christmas
www.iarelative.com/czech/xmas