What the Vedas teach? Can anyone give a brief description about the Vedas?

Over the millenia our acharyas and gurus have summed up the entire teaching of the Vedas and Upanishads in what are called the four Mahā-vākyas. These are the twitter version of the Vedas which are the foundation of Vedānta Philosophy.

1. Sarvam khalvidam Brahma — Everything that one can sense with the five senses and cognise with the mind is Brahman (meaning the “immensity” — the “Unified Field”, the “ground of Being”.)
2. Prajñānam Brahma — that Immensity or Unified Field is consciousness.
3. Ayam ātma Brahman — this individual Self (ātman) which is me in my essential nature as a ray of consciousness is one with that same Unified Field — Brahman.
4. Tat tvam asi — “you are that” – you, me and every sentient being is a ray of that Supreme All-pervading consciousness.