First of all, I thought I'd share a little fun. Here's a link to the full theme song from the show The Big Bang Theory. I highly recommend you take the time to listen to the whole thing if you haven't heard it.
Most people know that the Big Bang is the most popular scientific theory regarding the beginnings of our universe. Here's a brief summary of how we made it from the moments immediately following the Big Bang to today. Science is learning more every day, so no summary will ever offer a full picture, but this is still a good overview.
Once you posit that the universe started with the Big Bang, the question naturally becomes "What caused the Big Bang?" This next video looks at why we ask that question and how we try to answer it.
For anyone who wants to know even more and has a little more than an hour to dedicate to it, here's a link to a lecture given by Andrew Lange at UC Berkeley. There's a lot more detail here and is, in my opinion, relatively accessible for those who don't have a much of a background in science.