Answer:
Christians believe one day jesus will return to save all the people who happen to believe in him and send everyone else to hell for not believing his 2000 year old book. The earth will then be destroyed and all the christians will live forever in paradise and everyone else will eternally burn for what they did to god
Another Answer:
Doomsday is a prevalent human idea throughout the various religions/beliefs of the world that one day, this world will end or complete a cycle. The most popular of ideas this particular year are the Mayan Calendar and the Hopi Indian folklore.
The Scripture speaks of a 'end of the age' of the rule of man. It is described in many Prophetic books like Daniel, Ezekiel, Zechariah, etc and the specific timeline is spelled out in the Book of Revelation. Here there are the 7 Seals, Trumpets, and Vials that will occur until the 2nd Coming of Jesus Christ and the start of His Millennial Rule. The 1st Judgement of the 'firstfruits' will have occurred at His Coming again and afterwards the 2nd Judgement (all who never had a chance to hear the truth) for a short while. Then the final rebellion of mankind via the released Satan and the final 3rd Judgement (those incorrigibly evil who refuse to repent). After this the old will be cleansed by fire and a New Earth will become the Throne of God and His new spiritual sons and daughters - the vast majority of mankind that ever lived.