Dense hot matter composed of helium, hydrogen and deuterium was lumpy and expanding. Hawking calls this the most important discovery of our time or all time. At first everything was opaque, but then became translucent yielding a variety of galaxies. Suns are nuclear furnaces which burned helium and hydrogen into the heavier elements when they collapsed. At the singularity everything started - time and space.
Singularity is a mathematical term that says all is in one point - all the energy of the universe.
The amount of energy is undetermined. The point has no dimension in time and space. But quantum mechanics says it must have dimension. That's the limit of knowledge. Formation of solar system and earth.