It makes no sense. I don't think there's a way to present the answer, if there even is one, in any form of communication that we can even hope to imagine. Not even religion or a Big Bang theory can explain this.
how did this happen? a long time ago, actually never, and also now, nothing is nowhere. when? never. makes sense, right? like i said, it didn't happen. nothing was never anywhere. that's why it's been everywhere. it's been so everywhere you don't need a where. you don't even need a when. that's how every it gets. but yeah, quarks and stuff!
The universe was created by a process widely accepted by many different branches of the scientific community: https://en.m.wikipedia.org/wiki/1J74cf8/