Brahmâ was the first of the Devas, the maker of the universe, the preserver of the world. He told the knowlede of Brahman, the foundation of all knowledge, to his eldest son Atharva.

In plain words: Brahma, the first of the gods and the maker and keeper of the world, taught the knowledge of Brahman, the ultimate reality, to his eldest son Atharva. This knowledge is the base of all other knowledge.