Darwins theory of evolution by natural selection is not the Big Bang, Abiogenesis or Atomic theory.
The big bang is sometimes described as a titanic explosion that happened 13.7 billion years ago. 'Explosion' is a misnomer since the Big Bang happened everywhere at once and there was no pre-existing void into which the Universe erupted. Space and time and energy all came into being in the Big Bang. The Universe began in a super-dense, super-hot state 13.7 billion years ago and has been expanding and cooling ever since.
Just because you don't understand it, doesn't mean it never happened. Fortunately your belief isn't a prerequisite for the truth.
"It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition."