The current accepted model on the formation of the universe is the big bang theory. The big bang theory describes the universe as expanding, and originated in an infinitely tiny, infinitely dense point around 14 billion tears ago (gigayears ago or Gya). According to the theory, matter was not present at the beginning of time; there was only pure energy compressed in a single point called singlarity.
The fundamental statement of the big bang theory is attributed to Belgian Roman catholic priest Edouard Lemaitre in 1927. It was later supported by Edwin Hubble's demonstration of the countinuously expanding universe through his observation of galactic redshifts in 1929 and the discovery of the cosmic microwave background radiation by Arno Penzias and Robert Wilson in 1965.
The big bang was violent explosion which caused the inflation and expansion of the universe. At the moment, the universe was extremely hot that matter cannot yet exist. In a fraction of a second, four fundamental forces are formed: gravity (attraction between bodies), electromagnetic forces (binds atoms into molecules), strong nuclear force (binds protons and neutrons together in the nucleus), and weak nuclear force (breaks down an atom's nucleus and produce radioactive decay).
After three minutes, with the universe continuously expanding, it begins to cool down, allowing the protons and neutrons to fuse and form the nucleus of hydrogen and helium atoms. About 300 000 years later, temperatures became cool enough for hydrogen and helium atoms to completely form. At that point, photons (a tiny particle of light or electromagnetic radiaton) escaped and light existed for the very first time.
After 300 million years, stars and galaxies began to form as hydrogen and helium coalesce with the aid of gravity. The overall composition of the universe transitioned from light elements to heavier elements from the supernova as the temperature cooled down. This made solid particles, in the form of nebula, to exist. These nebulae would later on form the star systems and planets known today.