Thats not the big bang theory actually. It's more along the lines that everything started in a singularity, much like the theorized cores of
black holes where matter and gravity are virtually infinite. Something of that stature breaks down, shifts, it expands rapidly letting all its energy out. You have the release of the basic matter of the universe. Then through heat, gravitation and electric sources the basic elements of the universe change.
You have things such as abiogenisis occur on planets that create the building blocks of life, the formation of stars, etc.