The next upcoming Eid al Adha starts on sundown of Monday, July 19th ending at sundown on Tuesday, July 20th.
People are supposed to dress in their finest clothing to pray in a large open area or Mosque. Family and friends get together for a large lunch or late breakfast. Animals may be sacrificed as a symbolic reference to Abraham's willingness to sacrifice his only son. The meat is often divided into three with one third going to the relatives, another third going to the poor and the last third eaten directly by themselves to celebrate. Many people give to charities to support those who have less on this day.
The day is often referred to as Feast of the Sacrifice, which honors the willingness of Ibrahim to sacrifice his son Ismail showing submission to God. Eid al-Adha marks the end of the annual Hajj to Mecca.