If you're older then ten, you at least get the question, "How do you think the universe was formed?" at least once in your prepubescent life.
When people ask me that I simply say I believe in The Clock Theory. Then I get, "The Clock theory, what's that?". It goes a little something like this:
If you have a clock, and you take it apart, leaving all the necessary working pieces to make a clock, when will the clock reform itself? (In my terms: If you take a clock apart, when will it come back together?)
The answer is simple, the clock will come together when someone comes along and puts it back together. (No, this is not a bad punch line) It's just a sort of justification I give for the universe, and clocks always remind me of A Clockwork Orange
Disclaimer: No, I don't think you have to believe this, or agree with this. Hey, come up with whatever makes sense to you and apply it to your life.