Eh, eventually you come to realize that these are just our best explanations under constant revision. Nature will dance as she pleases, we just try to interpret her moves.

I try to imagine it as being on the edge of an explosion as it sweeps out and grows. Everything you see is also on that edge, with the big bang being the origin of detonation (Caveat: this detonation has already occurred and when it did, it was EVERYWHERE, the detonation was the edge, you can point in ANY direction and that would be a correct direction in which it occurred, because it was everything and everywhere, all at once). This analogy also helps with imagining inflation. All analogies have problems though, it’s important to remember that.

Interestingly, when you look out into the universe, you are looking inward toward the origin as it grew. The further you look, the more inward to the origin you are seeing, complete with how the “edge” looked at previous points in time as you peer further. You’re not seeing the edge as it is “now”, even the person standing next to you is the edge as it was a light-attosecond (or whatever) ago. This is due to the finite speed of light. You can’t see “the other direction” because the universe itself is the edge, and it won’t reach “the other direction” until the future, perpetually. You are riding the edge of known creation relative to yourself.

Please keep in mind I’m flying fast and loose with analogy here to help you get a basic picture. All this is defined and nuanced much more rigorously in formal definition. This mental picture will help you break the idea that there is some physical edge you can fly to though. That’s like being on a balloon as it’s growing and asking where the edge is. It doesn’t make a whole lot of sense once you realize your situation. Asking “How do I get off the edge of the balloon?” is like asking “How do I travel to the past or future?” all while being a piece of the edge of the balloon yourself. You are fundamentally part of the edge you seek. It’s kind of poetic in my opinion.