Short answers, pulled from the story.
The Vedas are a large body of religious texts originating in ancient India, composed in Vedic Sanskrit. They are the oldest layer of Sanskrit literature and the oldest scriptures of Hinduism. There are four Vedas: the Rigveda, the Yajurveda, the Samaveda and the Atharvaveda.
The Vedas have been orally transmitted since the 2nd millennium BCE. The oldest part, the Rigveda, was composed most likely between about 1500 and 1200 BCE in the Punjab region, while the other three Samhitas date to roughly 1200 to 900 BCE. The Atharvaveda was compiled last, probably around 900 BCE.
Each Veda has four subdivisions: the Samhitas, which are mantras and benedictions; the Brahmanas, which are commentaries on rituals, ceremonies and sacrifices; the Aranyakas, texts on rituals and symbolic sacrifices; and the Upanishads, which discuss meditation, philosophy and spiritual knowledge. Some scholars add a fifth category, the Upasanas, meaning worship.
The Vedas were orally transmitted and written down only after 500 BCE, yet only the orally transmitted texts were regarded as authoritative because of the emphasis on exact pronunciation. Witzel suggests early attempts to write them failed and led to smriti rules explicitly forbidding writing them down.
Apauruseya means not of a man, superhuman, and impersonal, authorless. Hindus consider the Vedas to be revelations of sacred sounds and texts heard by ancient sages, the rishis, after intense meditation, rather than works composed by human authors.
Sruti means what is heard and refers to the Vedas and their embedded texts, including the Samhitas, Upanishads, Brahmanas and Aranyakas. Smrti means what is remembered and includes texts such as the Bhagavad Gita, the Bhagavata Purana, and the epics Ramayana and Mahabharata.
The Rigveda is the oldest of the four Vedas and the oldest extant Indic text. It is a collection of 1,028 hymns and 10,600 verses organised into ten books called mandalas, dedicated to deities such as Agni, Indra and Soma.