The First World of the Navajo creation stories is the Black World, or Nihodilhil.
In this world, First Man and First Woman come to an understanding of space (the four corners of the world), the elements, and color (the colors of the elements), and other beings than themselves. They understood maleness and femaleness through the Black cloud and the White cloud and everything that the clouds represented. In this world, First Man and First Woman meet each other, and decide to go through life (existence?) together. Together, they learned that they were not the first beings in that world, and that there were many other beings. I do say beings, not simply in a philosophical sense, but rather because they are said to only have the form of man and woman, but not yet man and woman fully. As more and more beings appeared and joined the First Man and First Woman, the world was small, and thus became crowded, so they moved on to the next world.