For anyone who struggles with the idea of multi dimensional Universes the idea is basically that our universe is a Cosmic string that has collided in 11 (or so) Hyper Dimensional space with another Cosmic String (or,as I think, Five of them) and the resulting massive energy of the Hyper Dimensional pile up was the Big Bang.
Now the idea of more Dimensions then we can detect may sound strange but I put it to you that there are things in the Universe that were until only a few Years ago were unknown, Black Holes in space, Radio waves (You can not see these but they are still there!),Neutrinos and so on.
So if we can accept the premise that the Dimensions actually exists we can move on to String Theory, this Theory has the idea that there is a limit to how small matter can be, if for example we start with a Atom of Hydrogen and take it apart we find it is made of Electrons and A Proton ... now Disassemble the Proton or electron and we find it is made up of smaller sub partials and energy (Quarks......Star Trek fans fav Bar Tender!).
Now how far can we keep looking for smaller and smaller objects..... String Theory has the idea that at the smallest level the objects are in fact open and closed Strings or bands of potential energy vibrating in the 11 Dimensions and it is the way they move or vibrate that gives them their properties.
And it is they way they interact that makes the Universe work in the way it does.
Now if you could capture a String and pump Massive amounts of energy into it it would expand like a Balloon, or more like an unburstable Tyre inner tube...
Imagine what would happen to that..
..as the energy expands the Closed String or Band it starts to look like A Balloon.
The hole in the center closes and the outer surface expands outward....
... this is what many think happened to create our Universe, a closed string moving at Hyper Light Speeds though Hyper Space collided with one or move other Strings and the energy of the collision was pumped into and thus expanded the String or Strings (Big Bang).
Hope this helps!