I have posted videos before that attempt to explain the big bang theory and the beginning of the universe but with concepts as big as this, it never hurts to reinforce the ideas. These are things, after all, that the top minds in theoretical physics are struggling with so you (and I) can't be blamed if it takes a bit of repetition to wrap our heads around it.
Here is a five minute video from Kurzgesagt that attempts to explain what, exactly, happened in those early moments and what flowed from there. It cannot explain what happened before that because no one knows (if you can figure it out you've probably got a Nobel Prize waiting for you). It does, however, explain what sort of answer they are looking for.
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