Eid ul-Fitr is celebrated on the first day of Shaw'waal, at the completion of Ramadan. Shaw'waal is the 10th month of the Islamic calendar. Fitr' means to break and it signifies the breaking of the fasting period and of all evil habits.
The reason behind keeping fast during the time of Ramadan has reference to the legend of the Prophet Mohammed. He left Mecca and undertook a journey to Medina in 622 AD, where he joined with the other Muslims who had migrated to Medina to escape persecution in Mecca. It was during this time that he had fasted for three days. Years later when he received a revelation from God it was stated that followers of the Islam faith must undergo fast for a certain number of days every year. According to this Islamic belief, fasting helps to develop self-control and a means of coming closer to Allah. It also helps in purifying one's soul.
It is a show of joy at attaining spiritual prosperity after going through a month of fasting. Muslims turn out in the thousands, in local mosques to offer the prayer for Id. There is a lot of excitement surrounding the celebration of this festival as children and other family memebers wear their best and new outfits, engage in visiting each other and celebrating with good food and sewai. Eid is a public holiday and is celebrated all over India. It is even common for non-Muslims to visit their Muslim friends and neighbours on Eid to convey their good wishes and eat sweets like sewai.