The way I see it, God exists outside of this plane of existence, if you imagine the 4 dimensions, width, depth, height, and even time, a possible multitude of dimensions can certainly exist beyond these.
Imagine a being that is outside of all of this yet has complete control of everything, like the author of a book, writing and creating what they see fit. Inside of the story, the characters exist in their world the author has written, time is progressing normally for them but for the author and any other observers reading, they can freely go between pages, read the same sentence over and over, and the author can change and edit anything they wish. The characters within would never know about the existence of the author unless the author specifically wrote themselves in to the plot.
If this is in any way accurate to how God has created the universe this would explain how God is not only infinite but how he can be everywhere all at once and how he can easily listen to every prayer we pray and interfere with our existence creating miracles, or things that happen that can't be explained with any form of knowledge of our natural world.
Scientifically, We can not create or destroy matter, yet if the author writes it, aka God, then things can enter and leave this existence as he pleases.
Of course, this is a very rudimentary speculation of how God might be able to do the things he does and it doesn't take in to account the concept of free will. I do believe in free will but I realize it's a very difficult topic to explain, there's no way currently with our scientific tools to "measure" free will, yet I believe the behaviors of humanity can be seen as somewhat of a "Miracle" in itself, mainly in that we humans seem to do things that natural selection would reasonably never allow in other species of animals.
So yeah, long story short, God is infinite and can exist before and for all time because he himself exists outside of time itself and space for that matter. This is only my personal view but I'm not the only one who inks the same way. I hope What I said can help paint a clearer picture of how such a thing could be even possible.