Big Bang Nucleosynthesis

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Not all the atoms that surround you and compose your body came from stars. A small but nontrivial portion of them were forged shortly after the Big Bang, when the entire universe acted like an endless thermonuclear reactor. You can read more about that here:
Big Bang Nucleosynthesis

Carl Sagan wasn't telling the whole story when he said "We are starstuff." When the universe cooled off sufficiently for energy to crystallize into the humdrum particles that compose ordinary matter there were only protons and electrons, the stuff of hydrogen, at first. Within a few milliseconds those particles started bonking into each other and rearranging into the heavier stuff of helium, lithium, and beryllium, and this continued until the reaction was too cold to continue a few minutes later. While the scales of energy and mass are beyond all hope of human comprehension early in the universe, the timescales are easily understood in terms of ordinary life, somewhere between the blink of an eye and a clip from Top Gear.

I don't know very much about quantum physics, and I confess that much of the nuances of nuclear physics in the article are lost on me. Protons, neutrons, and heavier aggregates collide. Sometimes they merge, sometimes they split, sometimes soaking up energy from their surroundings and sometimes releasing it in the electromagnetic sea. I understand that this happens, but can't give a good explanation for what really drives it and its odd quirks. Why is helium-4 so inert and deuterium so ready come apart? Why does tritium glow with radioactivity while her daughter helium-3 is so quiet? Why are there no easily-formed stable nuclei between beryllium and carbon? The one part that makes perfect sense to me is that almost no carbon was formed in the Big Bang. The triple-alpha process requires three helium nuclei to arrive at the same place at almost exactly the same time, an event of such serendipity I'm amazed it ever happens at all. But happen it surely did, over thousands of years, in the stars that came after. The stuff of airships is still harmonizing into the stuff of diamonds today in stars close to the end of their main sequence lives.

As simple as many of the basic physical laws of the universe seem to be, the complexity of the way they come together to compose the forms around us is the stuff that awe is made of. Bizarre as it all is, Big Bang and stars and planets and comets and all that, the system does seem to work. We're here, after all.