The two official holidays of Islam are Eid Al-Fitr and Eid Al-Adha. Eid Al-Fitr is the celebration marking the end of Ramadan, the month of fasting. During the occassion, it is common for Muslims to give Zakat, one of the five pillars of Islam, which is a charitable donation of your wealth to the poor and needy. The second official holiday, Eid Al-Adha, is celebrated on the tenth day of Dhu al-Hijjah. This celebration lasts four days, and is a remembrance of Abraham's willingness to sacrifice Isaac for God. It is custom for Muslims to sacrifice a sheep, and distribute the sheep's meat among family, friends, and the poor.
Ramadan, is another Muslim celebration, which commemorates the first revelations of the Quran to Muhammad. This celebration typically lasts a month, where Muslim's fast from dawn until sunset. The fasting is a restraint from food, drinking liquids, smoking, and engaging in sexual relations. Each year the start of Ramadan, follows a lunar calendar, not a typically 12 month calendar. Because of this, the start of Ramadan usually jumps ahead 11 days each year. For example, if the start of Ramadan was August 1st this year, next year the start could very well be August 12th. Ramadan will then last for 29 to 30 days.