Belief in Doomsday is one of the fundamentals and pillars of faith. It is the day when everyone is to get recompense and punishment for one's work and has to go to heaven or hell according to one's deeds. This is the reason each and every Prophet warned his people of the Day of Judgement.
As for the knowledge of the time of Qiyamah (End of the World) , it has not been given to any angel or Prophet. Nobody besides Allah knows when the final hour is.
The Quran states, O Prophet the infidels ask you about the time of Qiyamah. So tell them that it's knowledge is with Allah only. (Surah Luqman)
However certain events are going to take place prior to the coming of the final hour. These events are known as the Signs of Qiyamah. All the Prophets informed their people of the signs of the final hour. Our Prophet Muhammed being the last and the seal of Prophets, knowing that Doomsday is to come upon this very ummah, explained clearly and in considerable detail the signs of the final hour to the extent that sometimes he would lecture his companions all day on this subject.
Abu Zaid (R.A.) says, 'The Holy Prophet sat down on the pulpit after Fajar Prayer and began a deliver a long sermon until the time for Zohr prayer came. After saying the Zohr prayer he again sat on the pulpit and began the sermon, which continued till Asr prayer. After the Asr prayer he resumed the sermon so much so that the sun set. he related whatever happened in the past and also related in detail whatever is to happen in the future. Those amongst us who had good memories retained many things.' (Muslim)
The signs of the final hour can be divided into two groups.
1) Minor signs
Minor signs are events of normal nature prophesised by our Prophet Muhammed to take place before Qiyamah like the consumption of alcohol, lifting of knowledge and prevalence of ignorance and immorality and signs of this nature. The majority of the minor signs have appeared while some are occurring and some will appear with major signs.
2) Major signs
Major signs ae events of extraordinary nature prophesied by our Prophet to take place before Qiyamah like all the events mentioned in the following hadith narrated by Hudhaifa ibn Usayd that the Prophet said, 'The last hour will not arrive till you have seen ten signs. He then mentioned the Smoke, Dajjal, Beast, Rising of the Sun from the place of it's setting, the Descent of Isa, Ya'juj Ma'juj, Three Landslides, one in the East , one in the West and one in the Arabian Peninsula after that a Fire would spread from Yemen and drive the people to their place of gathering.' (Muslim)
All Praises belong to Allah, Lord of all the world.
(More information refer to http://www.inter-islam.org/faith/Majorsigns.html#intro)