It's a long lasting, constantly evolving, multi-versal fluke.

We can't see, experience, or detect most of the universe — read: existence — let alone measure it. That pretty much means, to me anyway, we can't explain it.

Explaining existence, then, is limited to explaining my own perception of existence. To be brief: The things that exist got here the same way we did and use the same materials and rules. Conscious beings stay in the universe by maintaining consciousness; for us, that generally means being alive, awake, and alert — in that order. Upon death, consciousness ends, or departs, or continues (no one knows) and our corporeal form goes back to existing as atoms in other states within the environment. Present existence, then, pregnant by the ghosts of all existences that has gone before and is carrying to term all existences that will exist after. It's an endless, cyclical flow of atoms, energies, and absences. A crossroads of Space and Time culminating in experiential states and chains of causality. Billions of years in a blink.

Other conscious beings may operate or perceive differently. We can't individuall confirm or know. That's another of those rules.

That said, we only get to ride this existence thing for a short time. Build up your XP and use your one and only life doing good. Not necessarily well, but good.

Imagine standing outside of Time and Space and making a divine survey of the grand tapestry of the possible. It would look like math painted onto bubbles that glow from within, I think. That's what Existence may be.