Laylat al Qadr is the holiest night in the month of Ramadan 
  Also known as the Night of Power. It is believed the holy book of Muslims, Quran was sent down from heaven on this night. 
It comes in the last ten days of the month of Ramadan. Although there is no exact date of lailat al qadr . It is among the last five odd days . it can be 21st, 23rd, 25th, 27th, or 29th. 
The people with highest knowledge claim that it Is the 27th day of Ramadan. This year lailat al qadr will be celebrated on 12th of June 2018.

 The significance of Laylat al Qadr 
It is believed that the people who worship Allah on this holy night will have all their sins forgiven. They also get sawaab of 1000 months of worship. There is a complete chapter in Quran than throws light on the importance of the night of power.  
It is also believed that on this night the moon shines brightly without any rays and the sun will rise without rays, the night is full of peace. The holy Quran was revealed to angel  Gabriel on this night.
He then conveyed the complete 600 pages book to  Prophet Muhammad verse by verse in a span of  23 years. 
 Rituals of Laylat al Qadr

The importance of reading the holy Quran in this month is because it was revealed to Prophet Mohammad on this day itself. Therefore, they pray, read Quran and ask for forgiveness. They worship Allah all night. The best teachings are taught in madarsaas and hadees is discussed.