During Christmas you can collect new resources -- bells, snowballs, xmas balls, candy, tree cones -- to use to build limited edition structures. These new structures can be found in the 5th build tab or by clicking on the administration building. You collect the resources by clicking on the snowman couriers driving around your Vegas. The resources you've collected can be viewed in the Resource tab in your warehouse.
Once you build the Christmas Tree, you will receive a tree cone as a gift which you can use to send the Snowman gift to your friends. The Christmas Tree gives you 1 gold coin and another tree cone every ? hours. When you tap the Christmas Tree, it will start snowing in your Vegas. Making it snow before you click on the snowmen couriers will increase your chance of receiving one of the Christmas resources. There are also new awards and gifts to send your friends.