I don't think they know yet....

Currently the most accepted theory is that the universe began as a singularity.. (The Big Bang).... from that space was 'created'. Which means... there must be a point, location, where that initial birth took place.

The expanding universe, where all things are moving away from each other, is actually one of the things I can picture in my mind.... which is great except - then they have to toss in that 'space is bent' stuff. Meaning from any 'point' in the universe if you were to travel away in a 'perfectly' straight line you would eventually end up where you began. THAT I can't see in head. But this is more 'iffy' than the Big Bang.