There were fluctuations in the chaos of our infant universe. In any liquid or gas, Brownian Motion occurs; this is why milk will eventually disperse through your tea even if you don't stir your cuppa. This motion causes random fluctuations, and without these events the galaxy would never have formed, as matter would have been even distributed throughout the universe. All the ionised matter cooled, the protons, electron and neutrons started to form atoms. Nearly one hundred per cent of these atoms were hydrogen and helium, and none of the heavier elements, like oxygen, iron & carbon, were formed. This is not a universe where 'complex' molecules exist; there is no water, no salts, and no metals. Of course, there could be no life as we know it.
Gravity Works! (The Universe learns about the lightness of being.)
So, we have ended up with 'clumps' of matter, mainly hydrogen and helium, swirling and twisting in space. Gravity acts on these individual clumps, causing them to condense. As the matter condenses, it begins to pivot around its centre. Have you ever watched how an ice-skater achieves a fast spin? As they rotate, they draw their limbs in close and conservation of energy mean the kinetic energy has to go somewhere. The same thing happens to the condensing matter…it begins to pick up speed, and rotation increases. Spheres and discs are the natural products of the conglomerating, spinning matter.
Heavy Metal (Or, the Universe learns how to Rock!)
The first suns were the furnaces that baked heavy elements out of hydrogen and helium. Only the tiniest proportion of the matter was converted, in the intense heat and pressure of these solar ovens, but enough converted to make the some of the suns' unstable.
So, every atom and molecule in your body once existed within a sun; it had to, or you wouldn't be able to exist. You know, you hear about people that spontaneously combust…maybe the atoms remember their previous incarnation, and up they go! (Just my little joke.) Our Earth and everything on it are part of a third generation cycle, with each cycle increasing the complexity of elements. One can't help but wonder what the next generation will be like.