The most important Navratri festival of the Hindus is celebrated four times a year but the Mahanavratri festive season also known as Sharad Navratri begins on 1st October this year. It is celebrated at the beginning of Spring and Autumn. The dates of Hindu festivals change as they follow the Lunar calendar. The literal meaning of Navratri is 9 Nights.
During these 9 days devotees worship the Goddess Durga in her 9 forms and on the 10th day Hindus celebrate Dushehra or Vijayadashmi. The significance of the festival reaches far beyond the colourful costumes, singing and dancing. The Mother Goddess Durga the absolute creative energy of the Universe is worshipped resolutely in her various forms and is known by slightly different names in various regions. The rituals too differ from State to State.
Many people fast during these 9 days and do not consume non vegetarian food, alcohol or grains. The Scientific reasoning being that during this time of major seasonal change grains attract a lot of negative energies from the environment. This also helps cleanse the body and mind. People also worship the lunar constellations and pray for universal peace. They also pray for the 9 bodily orifices and ask for strength and restraint.
Often an uninturrupted lamp is lit in a clay pot called Kalash for 9 days. The pot called Kalash also represents the Universe and abundance of virtues. Some devotees sow cereals and grains in a pot in which the seeds start sprouting on the 9th day symbolising fertility.
The Navratri is celebrated with great fervour in Gujarat and West Bengal. In West Bengal Durga Puja during this time is the most important festival and in Gujarat the Mother Goddess is worshipped with Garba and Dandiya dancing.

Navratri (AAP) Source: AAP

Kalash (Getty) Source: Getty Images

Durga (Wikimedia/Jonoikobangali) Source: Jonoikobangali - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11774784
Happy Navratri and Dushehra which falls on the 10th day.