After his first vision in 610 A.D., up until his death in 632, Muhammad prophesied from time to time in a kind of trance. These pronouncements, in the Arabic language, dealt with many subjects such as: God's prophets and scriptures, God's mercy and punishment, death, the Last Day, good and evil spirits, laws of marriage, divorce, warfare, and so on. When Muhammad prophesied, his followers learnt the words by heart, or wrote them down on stones, bones, palm leaves, etcetera (for paper was scarce in those days). Finally all these pronouncements were collected and edited in a single book -- there is some difference of opinion among Muslims as to whether this editing was completed before or after the death of the Prophet. It is this collection of pronouncements which we know as the Qur'an -- the word "Qur'an" literally means proclamation or recitation.
But Muslims go much further than this. They believe that these are the words of God Himself, spoken through the lips of His Prophet, but not in any way coming from the mind and experience of Muhammad. They believe that the "mother of the Qur'an" (ummu-l-kitab) is in heaven, written by God Himself on a "guarded tablet" (lawhu-l-mahfuz); and that the angel Gabriel brought the tablet down to Muhammad -- so that the Qur'an which we have today is a copy of the "guarded tablet" in heaven. (cr. Q. 81).
But other Muslims, especially in modern times, would say that there is no Qur'an or tablet literally existing in heaven, but that these words are metaphors to show that God knew beforehand what He was going to reveal to Muhammad.

What is the meaning of Sura and Aya?

Sura means a "chapter" of the Qur'an. There are 114 suras, and Muslims generally refer to them by the name given to each one, rather than by number.
Aya means literally a "sign", and so a part of the Qur'an, generally one verse. Estimates differ, but there are commonly said to be 6,247 verses, 77,934 words and 323,621 letters in the Qur'an. To give an idea of its length, the Qur'an is a little shorter than the New Testament.
For recitation the Qur'an is divided into 60 sections, known as "hizb", which do not correspond at all with the chapter divisions.

Read the full article here: What is the Quran?