Vedas are eternal :
Vedas are the most ancient Hindu 'Books of Knowledge'. Primarily the word stands for 'knowledge' itself, and secondarily it refers to books. The word Veda is derived from the root 'vid' which means 'to know'. Thus the word stands for knowledge itself. Knowledge by itself is always eternal. Creation presupposes existence of prior knowledge. So knowledge was always there, and then came the creation. This knowledge which was already there is thus 'apaurusheya' i.e. not created by any human beings. There is infinite knowledge, and is available to be realised by any dedicated souls. So it is perfectly appropriate to say that Vedas are apaurusheya & anadi - not created by humans, and eternal.
Vedas are the basis of Hindu Dharma :
Vedas are the basis of Hindu Dharma. They are the most ancient existing scripture of the world. The Hindus rightly believe that they have been revealed by God himself, and are considered the ultimate & valid means of knowledge. Just as science is based on facts about the objects of the world, so also Hindu Dharma is based on certain eternal facts of life as revealed in the Vedas. Unlike other religions Hindu Dharma is not given out by any single person. The Vedas as we have today are a compilation of various matras as seen by different Rishis. So the analogy of science appears to be very appropriate. Even avatara-purushas like Sri Rama & Krishna liberally refer to Vedas in their teachings. There is a great sanctity about them.
Vedas are called Shruti :
Vedas are also called as Shruti. Shruti is that which is heard, again implying that they are something which were 'revealed'. No one ever arrogates personal doership for these divine scriptures. There are Rishis for various mantras, who were instrumental with their hard word & dedication to see these mantras. The word Rishis itself means 'Mantra-drashta', seer of a mantra. Earlier when paper or even palmyra leaves were not discovered or were in vogue, this knowledge was passed on to the next generation by word of mouth. The teachers revealed and the students heard them. So name 'Shruti' was justified this way too. There is a great tradition where the chanting & learning of these mantras is perfected to unbelieveable limits. There is no possibility of error of even half a alphabet etc. There are pundits who are taught to chant these mantras even backwards. A whole science of phonetics has been developed for this work.
The Sections of Vedas :
Vedas have two sections : Samhita and Brahmana. A very ancient commentator of Vedas Sri Sayanacharya says that these two sections together constitute Vedas. The Samhitas consist of prayers in metrical hymns called Mantras, and is also refered to as Mantra section. The Brahmanas are more of a commentary on these hymns, and are in prose form. This Brahmanas Section deals with Karma, Upasana & Tattva-Gyana. Sections dealing with these are called Brahmanas, Aranyakas & Upanishads. Upanishads are the philosophical parts of the Vedas, and reveal the nature of Self etc. Most of the Upanishads are at the end of Aranyaka Section, but there are exceptions. Isavasya Upanishad is in the Mantra or Samhita portion of Vedas.(It thus becomes very revered one). The mantras of Vedas were revealed to different Rishis at different points of time were collected & compiled into four parts (Rig, Yajur, Sama & Atharva) by one of the greatest sages of all times - Sri Veda Vyasa. Later he gave each of these Vedas to one of his desciples to carry them forward. Rig Veda was given to Paeil, Yajur Veda to Vaishampayan, Sama Veda to Jaimini, and the Atharva Veda to Sumantu.
Rig Veda :
Rig is derived from the word 'ric' which literally means 'praise or verse', especially 'a sacred verse recited in praise of a deity'. It describes metrical hymns which are meant to be recited loudly. The Rig Samhita is the biggest & oldest of all the Vedic Samhitas. It has 10 Mandals or Sections. There are 1028 Suktas in these Mandals. Suktas are a small group of Mantras, and have their own Devata, Rishi & Chhand. In all there are 10552 Mantras in Rig Veda, the first one being 'Agnimeda purohitam'. The total number of Rishis in Rig Veda is 403. The person who is the knower of Rig Veda is called Ritwik. There are two Shakhas (schools) of Rig Veda. They are : Shakla & Vashkala. Of these the former is more prevalent. Aitereya Brahmana is the well known Brahmana of this Veda. This Brahmana has an Aitereya Aranyaka which further has the Aitereya Upanishad.
Yajur Veda :
Yajur is derived from the word 'yajus', literally 'reverence, veneration or sacrifice'. It describes hymns in prose, and the mantras are basically used in sacrifices. There are two Samhitas of Yajur Veda. Krishna Yajur Veda & Shukla Yajur Veda. The Krishna Yajur Veda has three shakhas - Taittiriya, Kathaka & Maitrayani, while Shukla Yajur Veda has two schools - Kanva & Madhyandini. The mantras of this Samhita are called 'Yaju' and the knower of this Veda is called Adhvaryu. Yajur Veda is the smallest of all Vedas.
Sama Veda :
Sama Veda was basically meant for singing the mantras. There was a tradition of singing Sama in all Yagnas. Most of the mantras of Sama Veda Samhita have been taken from Rig Veda. The Samhita of Sama Veda has two parts - Poorvarchik & Uttararchik. The former section has six chapters with 650 mantras, and the latter section has 21 chapters with 1225 mantras. In all this Veda has 1875 mantras. The knower of Sama Veda is called Udgata. Some of the well known types of Sama-gana are - Brahat, Rathantar, Gayatra, Vairoop & Rajat.
Atharva Veda :
Atharva Veda has mantras to be used for various special purposes. The Atharva Veda Samhita has two parts. The Atharva & the Angirasa. The former is for sfter use while the latter has some harsh usages. Because of these two sections this Veda is also called Atharvangirasa, or in short Atharva Veda. The Samhita of this Veda has 20 kanda(chapters), 730 suktas amd 5977 mantras. The knower of these mantras is called Brahma, and has a very important place amongst all Ritwiks (knower of mantras of all Vedas). References have been found about for nine shakhas of this Veda, but as of today only one is available - the Pipalada Shakha. This Veda has great importance from the point of view of Adhyatma & Tattva-Gyana. The Brahmana Section of this Veda has the famous Upanishads like Mundaka and Mandukya Upanishad.