At least according to the standard model
here's what happened in the first three (or something like that) minutes after the Big Bang
10^-43 s--gravitation separates from other three forces (strong, weak, electromagnetic). Universe very, very hot and all particles carry tremendous energy. Quarks and leptons are not separate and quantum numbers are not conserved. During this time, a slight exess of matter over antimatter allowed the universe as we know it to keep existing.
10^-35 s--strong force separates, leaving electroweak force. Quarks, leptons, photons, etc. begin to condense into hadrons, including nuclear particles.
10^-6 s--most original hadrons disappear through continued collision with antiparticles. Universe has cooled too much for additional hadrons to be generated from photons.
10^-4-10s--leptons most common particles, thus this period is called the "lepton era."
A bit later (gotta love my scientific description of time), the "radiation era" began as annihilation between electrons and positrons allows protons and neutrinos to dominate the young universe.
Within a few more minutes, the "nucleosynthesis period" began and nucleons were fused into hydrogen, deuterium, and possibly lithium nuclei. As the universe became too cool for fusion to occur, rapid change ceased. Over the next few thousand years, the universe cooled enough to allow ionization energies to stabilize and the first light atoms were formed. Heavier atoms did not exist until the first stars were born and fusion could occur again.