Quran is a book revealed by Allah (Glory be to Him). It is a revelation sent to Prophet Muhammad (May Allah honour Him and Grant Him peace) for the span of approximately 23 years (13 years in Makkah and 10 years in Madina).
Qur’an (Koran) is an Arabic word which comes from four root words
1. “Qiraa’atun”: The most recited
2. “Qariyatun”: Things available
3. “Qarinatun”: Context and best structure
4. “Qaranun”: Joining
It is a book which is most widely read in the World. It contains all the information which is necessary for the success in both the worlds. It is structured in such a way that can be understood in the context. It also joins one incident with other, simple information to a detailed one.  
Scholars define the Qur’an as this: The Arabic speech of Allah that was revealed to the Prophet (صلى الله عليه و سلم) both in word and in meaning. It is collected between the two covers of the mushaaf, was narrated in mutawaatir chains, and is a challenge to humankind.
We can learn five important things about the Qur’an from this definition.
There are various names of the Qur’an given in Qur’an itself. For example Allah (Glory be to Him) called this Qur’an as Al-Furqaan (the Criterion between Truth and falsehood) in Qur’an. Surah Furqan 25:1, Surah Baqrah 2:185 and Surah Ale Imran 3:4, Al-Kitaab (the Book) in Qur’an. Surah Baqrah 2:2, Al- Wahi (the revelation) in Qur’an. Surah Anbiya 21:45 etc. 
The Qur’an is the literal word of Allah (Glory be to Him), the Almighty (Allah in Arabic), revealed to Prophet Muhammad (May Allah honour Him and grant Him peace) through the Angel Gabriel. “The revelation of the Book is from Allah, the Mighty, the Wise.” Qur’an.Surah Zumar 39:1.
The Qur’an is “a guidance for mankind… and the distinction (between right and wrong).” Qur’an 2:185 It provides direction to help mankind judge between right and wrong, without which, man would surely be in loss.
The Qur’an is the last scripture revealed by Almighty Allah (Glory be to Him), confirming what little truth remains in parts of previous scriptures and refuting and correcting fabrications and additions which have crept into current day versions of such scriptures.
“O you who have been given the Scripture! Believe in what We have revealed confirming what is (already) with you…” Qur’an.Surah Nisa 4:47. Further Allah (Glory be to Him) says that “..This day, I have perfected your religion for you, completed My Favour upon you, and have chosen for you Islâm as your religion”Qur’an.Surah Maidah 5:3.
The first few ayaah was revealed when Prophet Muhammad (May Allah honour Him and grant Him peace) was in Cave of Hira in Makkah. The first ayaat which were revealed was of Surah Surah Alaq.Qur’an Surah Alaq 96:1-5. It was revealed in the span of 22 years (lunar calender). Prophet Muhammad (May Allah honour Him and grant Him peace) took utmost care in compilation of Qur’an and made his companions to memorize and write it.
After the death of Prophet Muhammad (May Allah honour Him and grant Him peace) the companions came together and made it in one material. At the time of Usmaan(R), he ordered to make 7 replicas of the Qur’an and sent to the other part of his territory. Sahih Bhukari Vol 6: 510 and 514 
The Qur’an was not sent down as a complete book in one revelation; rather, the revelation spanned over a period of 23 years.
The Qur’an is the only religious sacred text that has been in circulation for a lengthy period, and yet remains as pure as the day it was revealed. Nothing has been added, removed or modified from it, since its revelation over 1400 years ago.
“We have, without doubt, sent down the Message; and We will certainly guard it (from corruption).”Qur’an.Surah Hijr15:9
Not only has the Qur’an been preserved in written form, but also in the hearts of men, children and women. Today, millions of people have memorized the Qur’an from cover to cover.
“And your god is One God. There is no god but He, the Most Gracious, the Most Merciful.”Qur’an 2:163
The most important topic mentioned throughout the Qur’an is the belief in the One, True God. God informs us that He has no partner, no son, no equal, and that none has the right to be worshipped except Him alone. Nothing is comparable to God and none of His creation resembles Him. The Qur’an also rejects the notion of attributing human qualities and limitations to God.
“And worship Allah and associate none with Him.”Qur’an 4:36
Since Allah alone is the only One worthy of worship, false deities and false gods must be rejected. The Qur’an also rejects the notion of attributing divine qualities to anyone or anything other than Allah.
“Indeed in their stories, there is a lesson for men of understanding.”Qur’an 12:111
This Noble Book reminds us that everyone will taste death and will be held accountable for all their actions and sayings:
“We shall set up scales of justice for the Day of Judgment, so that not a soul will be dealt with unjustly in the least…”Qur’an 21:47
Importantly, the Qur’an teaches that the purpose of life is to worship God alone, and live one’s life according to the way of life prescribed by Him. In Islam, worship is a comprehensive term that includes all actions and sayings (whether private or public) that Allah loves and is pleased with. Therefore, by doing what Allah commands, a Muslim is worshipping God and fulfilling his purpose in life. 
It is the only book which challenges the its reader to prove it wrong
There are various falsification test present in the Qur’an:
a. Challenge to Produce Surah like it. Qur’an Surah Baqrah 2:23
b. Challenge to show a contradiction.Qur’an Surah Nisa 4:82. 
a. Abu Lahab will not accept Islam. Qur’an.Surah Lahab 111:1-5.
b. Rome will win the War.Qur’an Surah Rum 30: 2-4. 
In summary, the Qur’an teaches mankind how to worship the One True God, hence fulfilling their true purpose in life, and attaining success in both this world and the next.
“Verily, We have sent down to you (O Muhammad) the Book for mankind in truth. So whosoever accepts the guidance, it is only for his own self; and whosoever goes astray, he goes astray only for his own loss.”Qur’an.surah Zumar 39:41