At the time of the revelation it was not written in a form of a book. Every body knew it by heart. Propher (SAW) let some of his companions write it down on cloth, bones, and animal fur. The scribes would then read their writing back to the Prophet, who would check it for mistakes. With each new verse that was revealed, the Prophet Muhammad also dictated its placement within the growing body of text. These writings were later collected and complied into a book after the demise of Prophet Muhammad (SAW)
There are 114 surahs in the Holy Quran. A surah is the Arabic Quranic word for a chapter. When a new surah comes up when you are reading Quran it means you finished a chapter and your starting a new one. Something else that is in the Quran areparas. There are thirty paras in the holy Quran. Paras are sections of the Quran divided in to thirty parts. Another thing in the Quran is a manzil. A manzil is a collection of ayats and short surahs from the Quranthat are recited as means of protection. Two major subjects explained in the Quran are about God and Prophet-hood.
For more details about Quran please visit http://islam.about.com/od/quran/a/Compilation-Of-The-Quran.htm