Answer:
The Big Bang
Step-by-step explanation:
The widely accepted theory of Universe Creation is the Big Bang Theory. According to the theory the universe started with a huge explosion(or expansion). Before that everything that we know was stored in a very small and dense area.
This explosion hurled the material in all directions. With time the universe started cooling and formation of atoms started with Hydrogen being the first and most abundant.
Slowly the stars, galaxies and other celestial objects started forming. The age of the Universe is estimated to be around 13.8 Billion years.