How does the big bang theory explain the origin of the universe?

It is by no doubt that our universe had had its own starting point but how it really started became a debate for the scientists over the past centuries. From theories such as Ekpyrotic theory, White Holes, Matrix theory, and Quantum theory, the Big Bang theory is the theory mostly accepted by scientists. According to the theory, the universe started as a singularity, that is, from a black hole under extreme gravitational pressure and expanded (instead of exploded) and cooled. Its cooling, according to the theory, is still happening now as of the moment.

The big bang theory is one possible description of the
origin of the universe.

Of all the possible descriptions that have been offered so far,
it does the best job of explaining the conditions we see in the
universe right now.  That's why it comes closest to being
accepted at the present time.