Ved are the oldest and original scriptures of Vedic Sanatan Dharm. There are four main Ved (Or Vedas) that were spoken by Brahm (or God). They are Rigved, Yajurved, Samved and Atharvaved.
Ayurved (oldest branch of medicine) is considered as the fifth Ved. The Ved are the oldest scriptures that are written in Vedic and divine language Samskrut. Ved were sung by God and were heard, memorized & composed in appropriate Samskrut hymns by the great sage Ved Vyaas. Vyaas was one of the incarnations of God Vishnu.
There are mainly four Veds:
Rig-Ved contains 1028 hymns (10,589 verses, 10 Mandal or segments) that are dedicated to 33 different gods. The most sung gods in Rig-Ved are gods like Indra (rain god; king of heavens), Agni (fire god), Rudra (storm god; the 'howler'), Som (the draught of immortality, an alcoholic brew).
The Yajur-Veda or the wisdom of sacrifices lays down various sacred invocations (Yajur) which were chanted by a particular sect of priests called Adhvaryu. They performed the sacrificial rites. The Veda also outlines various chants which should be sung to pray and pay respects to the various instruments which are involved in the sacrifice.
The Saam-Ved is a collection of Shlokas, derived from the 8th and 9th books of the Rig-Ved. The Saam-Ved verses are for the Brahmans who officiate at the rituals of the Som ceremonies. There are instructions in Saam-Veda about how particular hymns must be sung; to put great emphasis upon sounds of the words of the mantras and the effect they could have on the environment and the person who pronounced them.
The Atharva-Veda (the wisdom of the Atharva) is called so because the families of the Atharva sect of the Brahmins have traditionally been credited with the composition of the Vedas. It is a compilation of hymns but lacks the awesome grandeur which makes the Rig-Veda such a breathtaking spiritual experience.