Eid-ul-Adha ('Celebration of Sacrifice'), also known as the Greater Eid, is the second most important festival in the Muslim calendar. It marks the end of the Hajj, the annual pilgrimage to Makkah (Mecca). It takes place on the 10th day of Dhul-Hijjah, the last month of the Islamic calendar. Although only pilgrims to Makkah can celebrate it fully, Muslims elsewhere also mark the occasion of Eid-ul-Adha.
The Hajj is the Fifth Pillar of Islam and therefore a very important part of the Islamic faith. All physically fit Muslims who can afford it should make the visit to Makkah, in Saudi Arabia, at least once in their lives. Every year around 2 million Muslims converge on Makkah. They visit a shrine in the city known as the Ka'bah, built by Ibrahim (Abraham) and Isma'il (Ishmael) at the command of Allah (God). It is a place for all who want to reaffirm their faith.
Eid-ul-Adha celebrates the occasion when Allah appeared to Ibrahim in a dream and asked him to sacrifice his son Isma'il as an act of obedience to God. The devil tempted Ibrahim by saying he should disobey Allah and spare his son. As Ibrahim was about to kill his son, Allah intervened: instead Allah provided a lamb as the sacrifice. This is why today all over the world Muslims who have the means to, sacrifice a sheep (alternatively a goat or cow can be used), as a reminder of Ibrahim's obedience to Allah. They usually share out the meat with family and friends, as well as the poorer members of the community. In Britain, the animal has to be killed at a slaughterhouse.
Eid-ul-Adha is a 1-3 day celebration and in Muslim countries is a public holiday. It starts with Muslims going to the Mosque for prayers, dressed in their best clothes, and thanking Allah for all the blessings they have received. It is also a time when they visit family and friends as well as offering presents. At Eid it is obligatory to give a set amount of money to charity to be used to help poor people buy new clothes and food so they too can celebrate.
This information is just a google click away at:
http://www.bbc.co.uk/schools/religion/islam/eid_haj.shtmlif you really want to know.