First of all, perhaps you are slightly confused because you think that the Quran was revealed as a book or that it was given to Prophet Muhammad (peace be upon him) all in one go. In fact, the Quran was revealed to Prophet Muhammad (peace be upon him) by the Angel Jibreel (Gabriel) over a period of twenty three years.
Some people wishing to cause mischief suggest that Muhammad (peace be upon him) actually made it up himself. Muhammad (peace be upon him) was a simple, unlettered man. He could neither read nor write and knew nothing of poetry or the finest intricacies of the Arabic language.
The revelations were given to him orally. In other words, they were not written down but he heard them and then memorized what he had heard. Those around him then learned by heart exactly what he told them. As the Muslim community grew, more and more people were learning the verses by heart and could correct one another if someone made a mistake in the recitation.
After some time, the words of the Quran were written down and it is those words, written down fourteen hundred years ago, that have not been altered in any way since. In fact, if you were to pick up a copy of the Quran from any of the last fourteen centuries and from any part of the globe you would find that the words are exactly the same.
One of the reasons the words have not been altered is partly because of the Arabic language. The Quran was revealed in Arabic [the language of Muhammad (peace be upon him)] and it remains in Arabic to this day. The meaning of the words has been translated into many languages, but the original Arabic is the true Quran and it is to this that Muslims refer whenever there might be a dispute.
Muslims believe, by the way, that one of the reasons Christians have come to believe what they believe today, is that they have translated from one language to another and then to another, losing the meaning of the original - which no longer exists.
To get back to your question, the verses of the Quran were revealed over twenty three years and in response to particular situations at the time. During Ramadan of each year, the Angel Jibreel would recite all the verses revealed so far with Muhammad (peace be upon him). At the end of his life, it was revealed to Muhammad (peace be upon him) the order in which the verses were to be written down.
This is a spectacular event because no one could have known twenty three years earlier what the final Quran would look like, yet the final version was a masterpiece. Parts of verses and chapters, revealed many years apart, were put together and were found to rhyme and have themes and sub-themes with their following verses, which no one could have predicted. What had seemed to be the answer to a particular section many years before, now had a universal meaning.
It is rather like a building site. Anyone looking at the site would just see heaps of bricks, sand and cement. Only the architect would know what the final building would look like. In the same way, the verses of the Quran appeared like random revelations, yet when they came together at the end, the Architect of the Universe revealed something magnificent and extraordinary. What had been revealed to Muhammad (peace be upon him) was in fact God's final revelation to mankind, which would remain unaltered for ever.
Even teams of scholars and authors could not have produced such a masterpiece had they worked together for years, yet this unlettered man (peace be upon him) produced something the world had never seen before.
Finally, it is worth remembering that the Quran was revealed to be listened to. When recited well it has a beauty that touches the heart, even if non-Arabic speakers can't understand the meaning of the words. The words themselves seem to have a power which transcends human language.