The Big Bang, according to scientists, took place between 10 and 15 billion years ago. It took awhile (ooo… three minutes or so) for protons to actually come together and form helium, and longer for the electrons to actually settle in their orbits around these atoms. For awhile, all there was was hydrogen and helium… eventually, EXTREMELY large clouds of gas condensed under the force of gravity and formed galaxies and stars. These stars produced the heavier elements: carbon, oxygen, nitrogen, etc. (All the matter you see around you originated in a star… your computer, your chair, you.) As stars blew up or died out, there was a lot more dust and gas floating around, which condensed, and formed more stars and the planets. I don’t know what “generation” star the Sun is, but you get the idea.
I hope this all makes sense to you… But realize that after 10(-43) seconds, scientists can describe the universe relatively well, but not before that.
A little sidenote, due to the astronomical distances that we can see in space, we end up actually seeing into the past, since the light can only travel a finite speed. I forget exactly how far back we can see… but… certainly, billions of years.