Hello.

I think that the answer you are looking for, is Big Bang Theory.

The theory explains how the universe actually came into existence from a very tiny, dense state that it is today. In short, it talks of the expansion of the universe, quite contrary to our belief that it resulted from an explosion that has been proved incorrect in recent times.

If you are interested to know further, you can actually look up books online on this topic. Since the Big Bang theory covers many domains of science, it wouldn't be possible to explain all of it here.

Hope this helps.