This is not an absolute answer as, so far, nobody has one which all honest objective rational people can comfortably accept. But, it attempts to lead via a master of the art either to an answer that will make you happy (two available) or to the only other choice.
This question, in a multitude of forms is known to have been being asked for millenia, at least, and probably since anyone could conceptualise the question.
eg we "know" that a slime-mould, fly, or bird cannot ask this question, we think it unlikely that any "non-human" primate can and we hope both that some cetaceans can and that all can't deep-ending who we are.
Based on having looked at some length on various occasions, I know that there is much discussion on this.
As far as I can see, as a Christian, BUT really wanting to know about the reality about us (despite eg Krauss's jibes), there are essentially 3 answers. Two of these must be wrong and the 3rd is somewhere near your personal event horizon - but whether inside it or outside it may never be certain :-).
The 3 possible answers are
Something always has been.
It all just happened absolutely completely by itself out of utter utter nothingness.
(That's the empty 'void' of space time itself - not this pretend empty vacuum with a quantum foam of particles popping in and out of existence to keep Heisenberg happy THAT is not 'empty space' that had to be created from 'nothing' ex nihilo
A metaphysical "shell" exists which all reality is 'inside', in which the concepts of 'always existed' and 'came from absolutely nothing' are not the ludicrous impossibilities that they are inside 'reality'.
So:
You need to convince yourself that the 1st two (always was / all just happened) are utterly untenable in any reality that makes sense (and all those that don't as well). If you cannot conclude this then accept one or other (or both) and be happy - there's nothing to explain, move along, these are in fact the ones you want. There are many people who do seem able to do this - including the great Lawrence Krauss - more of him below. I do not find the arguments intellectually tenable (of the ones I understand or think I understand) and I hope to understand more of them. But I'd be surprised if anything changed (Krauss nothwithstanding). That's NOT a 'religious observation' but it does lead to a 'metaphysical' conclusion.
In the SE answer Stephen Hawking says universe can create itself from nothing, but how exactly? reference is made to this ~= 1 hour video by Lawrence Krauss (go to start for 2m intro by R Dawkins if desired).
If at the end of the 1 hour video you are happy, stop.
If not, hair of the dog may work - Amazon will sell you these books of Krauss's
Including A Universe from Nothing: Why There Is Something Rather than Nothing
Their summary:
Bestselling author and acclaimed physicist Lawrence Krauss offers a paradigm-shifting view of how everything that exists came to be in the first place.
“Where did the universe come from? What was there before it? What will the future bring? And finally, why is there something rather than nothing?”
One of the few prominent scientists today to have crossed the chasm between science and popular culture, Krauss describes the staggeringly beautiful experimental observations and mind-bending new theories that demonstrate not only can something arise from nothing, something will always arise from nothing. With a new preface about the significance of the discovery of the Higgs particle, A Universe from Nothing uses Krauss’s characteristic wry humor and wonderfully clear explanations to take us back to the beginning of the beginning, presenting the most recent evidence for how our universe evolved—and the implications for how it’s going to end.
Provocative, challenging, and delightfully readable, this is a game-changing look at the most basic underpinning of existence and a powerful antidote to outmoded philosophical, religious, and scientific thinking.
Krauss says things that sound to me like cheating writ large to help make it invisible. But, what would I know? (Even knowing how much more he knows, it still seems like cheating). If you don't agree with me and find Krauss plausible, you have your answer. If you do agree you may want to look at option 3. Note that option 3 does not require "God as we know/don't know him/her/it, Jim".
It 'just' requires a "metaphysical" answer. If that is utterly inconceivable you may have 3 'impossible ' answers :-).
Video:
It's interesting to see how many of his academic puns seem to be completely missed by his audience.
Nice little dig in passing about certain model based theories at around 5-6m (some laughed).
