The word Veda has derived from Sanskrit word, Vid. Vid means to know so Veda means knowledge. The books in which the knowledge of ancient Indian culture and mystics are stored. The Vedas are the root and origination of VEDIC religion. Still there is no specific author of Vedas but it's a collection of dialogues communicated between the master and the disciple from time to time on any subject. The Vedas are considered to be the oldest book in the world. There is a lapse of time between the first mantra and the last mantra of the Vedas. Though the Vedas are one, they have been divided into four parts considering the subject and form of the mantras by rishi Ved Vyas. Thus, the knowledge has been divided into four Vedas, namely Rigveda, Yajurveda, Samved, and Atharvaveda.

Rigveda :

The Rig Veda is the book of Mantra. It contains the oldest (composed in archaic Sanskrit probably between 1500 and 1200 BC) form of all the Sanskrit mantras. It is built around a science of sound, which comprehends the meaning and power of each letter. Rig Veda contains over 1,000 hymns directed to the gods. The content of these hymns includes praises, blessings, sacrifices, and curses. The subject of the hymns is the personification of the powers of nature. Most Vedas consists of songs recited during sacrifices, and passages instructing priests, or Brahmans, what to do during the ceremony. The Rig Veda is the source of many Indian practices and philosophies

Yajurveda :

The Yajur Veda consists of hymns from the Rig Veda along with other hymns which when recited in the performance of a yajna / havan will enable the Soul or the beneficiaries to understand the universal truths of the Veda in any or all of the three planes of its meanings depending on the individual's stage of spiritual evolution. Though the Yajur Veda is associated with performance of Yajna for worldly gains, it is understood that the individual beneficiaries will ultimately evolve spiritually and subsequently undertake these Yajnas for the spiritual and material benefits of mankind as a whole. The Yajur Veda has two distinct schools of presentation and following as explained below

Shukla Yajur Veda:

Northern parts of India and has mantras in the form of the Veda and Brahmanas. The Shukla Yajur Veda is said to have been taught by the "Sun" to sage Yajnavalkya and hence the name "Shukla" or "White" Yajur Veda. Krishna Yajur Veda: Southern parts of India and has Veda mantras and Brahmanas intermixed - that is, the Brahmanas follow the mantras as explanatory notes in the Veda text itself. Since Shukla Yajur Veda is known as "White", this Yajur Veda has been denoted as "Krishna" or "Black" Yajur Veda. Both the versions are accepted as authentic and both schools are practised widely.

Samved :

The Sama Veda consists of hymns (many of them common with the Rig Veda) which when sung in the appropriate manner will strike a chord in enabling one to understand the universal truths and order of life depending on their stage of spiritual evolution. The source of the musical patterns of the Sama Veda hymns is derived from the vibration / sounds of the cosmos. This reveals that spiritual evolution can be achieved through music (by hearing as well as singing). The Indian music is said to have born from Samved.

Sama Veda has two parts, Purva-Archika (First Adoratona) and Uttar-Archika (Later Adoration), containing verses addressed to the three gods Agni (Fire), Indra (King of Gods) and Soma (Energizing Herb). The verses are not to be chanted anyhow, but to be sung in specifically indicated melodies using the seven svaras or notes. Such songs are called Samagana and in this sense Samaveda is really a book of hymns.

Atharvaved :

This Ved has special types of scientific experiments. It has two parts namely Atharva and Angiras. In the first part the experiments are very soft and mild but the second part has very aggressive experiments. It has very important suktas of mystics, spiritualism and philosophy too. Some practical knowledge has been included into this Vedas. It has in all 20 chapters, 730 suktas and 5977 mantras.

The Atharva Veda, when understood in the external plane, is generally known to contain hymns common to the Rig Veda including others for the sole purpose of performing "Magic" or to communicate with ghosts and spirits or for curing ailments. However, when viewed in the spiritual plane, the Atharva Veda expounds universal truths of the oneness of the universe, the way to live in communion with the world of evolved souls, to pray for a healthy life and finally to merge with the Supreme

Upnishads:

Upnishads are known as Vedant i.e. The end and last portion of Vedas. They are essence of the Vedas. Our Upnishads have influence Bauddha, Tao, Jain and China, Japan and other Asian thinkers. In all there are 108 Upnishads. There are no particular authors of Upnishdas because they are a compilation and edition of the dialogues took place between the master and disciple from time to time.

In ancient days there were Ashrams, which are said to be the school of philosophy in which philosophical and religious discussion held between the master and the king or the master and the disciple or even between two Rishis . All this dialogue have been compiled in this Upnishads. Adi Shankaracharya had considered 12 Upnishads as the main Upnishads out of 108. They are Ishavasyaupnishad, Kenopanishad, Kathopnishad, Prashnopanishad, Mundakupnishad, mandukyaupnishad, Taittiryaupnishad, Aitariyaupnishad, Chandogyaupnishad, Brahadaranyaupnishad, Svetasvataropnishad and kaivalyaupnishad.