"Yet, there is no center to the expansion; it is the same everywhere. The big Bang should be visualized as an ordinary explosion. The universe is not expanding out from a center into space; rather, the whole universe is expanding and it is doing so equally at all places, as far as we can tell"
I know you might be thinking, "How will a Middle Schooler answer me?!"... I am really a Middle schooler, but my brother in college gave me this answer to your question.
Hope this helps you out!