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>why there are something instead of nothing?
Well, the thing is we don't really know. We have various theories within the realms of physics, mathematics and so on that attempt to explain it as best it can (this is far too deep to go into here). For "materialists", this is how we explain the Why. Tl;dr it just does...things happened, the universe formed and the rest is history.
Then there are the philosophical concepts. These, again, are highly varied. It's really open to interpretation because (most) philosophy does not rely on empirical observations, it's just thought and speculation. Various philosophies have attempted to reconcile these issues. Kant tried to reconcile science and God through his transcendental idealism. The existentialists said there is no god of any kind. Camus, with his absurdism, said who cares, maybe God is or isn't, maybe there is nothing and nothing matters, just live and enjoy your life no matter what. And so on.
Then you've got the theological view, be it Christianity, Islam or some wacko fringe religion about UFOs or something. This is kind of like accepting that we don't know so you just decide to come up with some stuff to explain everything, most of which boils down to "well God(s) created it, that's that!" which, frankly, I think is such an empty thing to accept. You're just making things up with no hard truths and no known ways to prove the existence of any God or similar deity.
Since we don't really know, it's up to you to choose what you want to believe.