The Quran (also written Koran and Qoran) is the holy book for believers of Islam. Muslims believe the book was delievered to the Prophet Muhammad, by the Angel Jibril (Gabriel, in Judaism and Christianity), and it contains the words of God. The Quran is divided into 114 Suras, each of them divided into verses called Ayah (Arabic for sign or miracle).
There are two types of Suras: ones that were given in Mecca, before Muhammad made the Hijra to Medina. These Suras are more general, and often contain encouraging words for the Prophet and his believers, due to the persecution he suffered from the pagans. The Suras from Medina are more specific, and contain instruction and laws. The Islamic Sharia is based on these verses.
Suras are not organized by the order they were revealed to Muhammad, rather they appear in the book according to their length. Starting from the longer ones, with few exceptions.
During the middle ages of Islam, many theological debates revolved around the Quran. The Mu'tazilah school, affected by Greek philosophy and rationalism, considered the Quran to be created by God. The more conservative schools viewed the Mu'tazili position as blasphemy, and argued that the Quran is the word of God, a part of God, and therefore was not created, but always existed.