The month of Ramadan enjoys a intrinsic superiority over all other months of the year. It has a night better than thousand months according to the Qur'an: "Undoubtedly, we sent it down in the blessed and valuable night. And what you know, what the blessed night is? The blessed and valuable night is better than a thousand months. Therein descend angels and Jibrail (the Spirit) by the command of their Lord for every affair. That is all peace till the rising of the dawn." (Surah Qadr)
About the reason of revelation of this verse, it has been narrated by our Prophet (sallal laahu alaihi wasallam) that one day he talked to his Companions about a person of a past nation and informed them that he spent a thousand months praying the whole night and doing Jihad all day. So his companions felt very sorry that due to their short life they cannot get that status. Then Allah Subhanahu wa Ta'ala revealed this verse (Surah) and informed Muslims that though you have not been given long lives yet by praying on the Night of Power you can get the rewards more than a person praying one thousand months.
The Prophet (sallal laahu alaihi wasallam) also described several times the significant values of this night: Hazrat Anas bin Maalik (radi Allahu anhu) reported that the Prophet (sallal laahu alaihi wasallam) said that this month (Ramadaan) has approached to you, a night of this month is better than thousand months. One who failed to get the blessings of this is failed to get any blessings. And no one is failed but he who is truly disappointed. Allah Subhanahu wa Ta'ala promissed forgiveness to the praying persons in this blessed night: Abu Huraira (radi Allahu anhu) reported that our Prophet (sallal laahu alaihi wasallam) said that one who prays in this night with Imaan and with the intention of getting blessings will be forgiven. Anas bin Maalik (radi Allahu anhu) reported that our Prophet (sallal laahu alaihi wasallam) said that at the Night of Power, Jibrael (alaihis salaam) came down with a group of angels and prayed for mercy for the bondsman who is engaged in the worship of Allah Subhanahu wa Ta'ala sitting or standing.
How to find out Laylatul Qadr
It is narrated by Hazrat Aisha (radi Allahu anha) that the Prophet (sallal laahu alaihi wasallam) said: "Seek the Night of Power in the odd nights of the last ten days of Ramadan". This Hadith shows that the Night of Power falls on one of the odd nights of last ten days that is 21st, 23rd, 25th, 27th and 29 th night. But we have some other indications from the companions of the Prophet (sallal laahu alaihi wasallam) and Muhaddhiseen, that this should be the night of 27th of Ramadaan.Due to this it seems a general consensus among the Islamic Scholars towards the 27th night. However, it is better to keep vigil during all odd nights of last ten days to get the blessings of this precious night. The Du?a to be read during this night is "Allahumma innaka afuwuh tuhibbul afwa fa’fu anni". This Du?as was taught to Hazrat Ayesha Siddiqa (radi Allahu anha) by Huzoor (sallal laahu alaihi wasallam) himself.