The Big Bang Theory is the process explaining how the universe came about. It began to expanded from letting off hydrogen and helium. And expanded for many years letting off a lot of heat.
The planets forming
The whole big bang process started with a small little sopt in the universe which expanded over 13.7 billion years ago.
Within the first 3 mins of the explosion it was to hot to form atoms, charged electrons. The universe was just on big hot fog. Later on down the line about 300,000 years later, the elctrons began to combine with protons and neutrons, which formed atoms. Finally there was light.
About 1 billion years later based on scientist gravity came in causing helium and hydrogen atoms to coalesce making the planets we have now today.
Caused by the big bang theory we have every star, planet, sun, and galaxy we have seen in space today.