Pragâpati brooded over the worlds, and from them thus brooded on he squeezed out the essences, Agni (fire) from the earth, Vâyu (air) from the sky, Âditya (the sun) from heaven.

In plain words: Prajapati, the creator god, thought deeply about the worlds and drew out their essence. He got fire from the earth, air from the sky, and the sun from heaven.