Big Bang Timeline

Because the universe was so dense and hot at its very beginning, what we know about this portion is purely theoretical because we simply don't know how the laws of physics work at such immense temperatures. Technically, general relativity predicts that the universe was a compact mass concentrated into a gravitational singularity. However, general relativity isn't at all reliable at times that are as short as the Planck Epoch. The four fundamental forces -- gravity, electromagnetism, and the weak and strong nuclear forces -- that mediate everything was considered as one force at this time.

After the plank epoch, the universe went through an immense stage of inflation. Around this period, the universe cooled to the point that the four fundamental forces could be distinct and not unified. Technically, this can be considered its own period of the universe but as mentioned before, the universe has always been expanding rapidly so this period of the universe isn't truly that distinct. After about 3 minutes, the universe's temperatures cooled down significantly to about 900,000,000 K, which is still far beyond anything we've experienced in our daily lives. For reference, the Sun itself is around 5800 K, and being anywhere near the Sun would result in your almost instant disintegration. There were a few protons and neutrons created due to the very first few instances of the universe. However, after 3 minutes, they could finally combine to create deuterium, which is just a proton and neutron combined, along with other atomic nuclei, like helium and lithium. However, electrons weren't around yet so just atomic nuclei were being formed, not atoms themselves. This period of the universe where atomic nuclei formed is known as the big bang nucleosynthesis. Physicists have always been confused about how the universe can have so much helium just from fusion within stars. However, they often point to this period to note that there was probably more helium produced during this period of the universe than inside stars since the Big Bang.

A few thousand years out of the Big Bang, electrons start forming in more relative abundance but the universe is simply too hot for these electrons to possibly combine with the stray atomic nuclei. After 18,000 years or so, electrons can finally combine with atomic nuclei to form proper atoms. After this, the rest is history as these atoms slowly started forming in more abundance. Because of this, they eventually gravitationally attracted one another and formed molecular clouds, which gave rise to stars and eventually planets like our Earth.