In Russian, Happy/Merry Christmas is C рождеством! or Счастливого рождества!
Some Orthodox Christian Russians fast on Christmas Eve until the first star is in the sky that night. At this time they eat a porridge made from wheat or rice with honey, poppy seeds, berries, and nuts called Kutia which symbolizes unity. As a common superstition, that if they throw a spoonful of Kutia onto the ceiling and if it sticks it will bring them good luck and a good harvest. Following the meal, prayers might be said and people then go to the midnight Church services. They often don't wash the dishes until they get home from Church - sometimes not until 4.00am or 5.00am!
The New Year celebrations are still very important to Russians (sometimes more than Christmas).
This is when - when 'Father Frost' (Дед Мороз) brings presents to children. He is always accompanied by his Grandaughter (Snegurochka). On New Year's eve children hold hands, make a circle around the Christmas tree and call for both of them. They bring light to the Christmas tree.
Overall, it is a very festive season lasting from December 31st to January 10th.