We weren't there! What we do know is that "Something" happened. In science, they choose to call it "The big bang", and in theological circles they call it the voice of G-d. What would the voice of G-d sound like? We know from the Book of Exodus, Shmot in Hebrew, that for the little tiny bit of what the Jews heard at Mount Sinai, that it was powerful enough to kill everyone that heard it. Now, if we were to expand that to G-d playing in an empty space without the care of killing everything, then we can say that it would sound a lot like an explosion... BANG! Scientists estimate this time to have occurred around 15 billion years ago. Interestingly, enough according to Rabbi Isaac of Acco (13th Century Kabbalist), the account of creation would have occurred 15,340,500,000 years ago. The earth, or the start of life on earth, by the same standard is 2,556,750,000 years ago, also very close to the scientific estimate of when life began here.
There are actually two accounts of creation in Genesis (Bereshit in Hebrew). Chapter 1 talks about the start of creation in the 6 days or cycles, where G-d did not actually create the world, but put all of the components together that allow the earth to develop. After these 6 days, G-d allowed the universe to develop by itself, as all of the laws of nature and matter had been established. Each of the six days, or cycles, brought something new into existence. The fifth cycle being the one that brought about life approximately 2.5 billion years ago. Interesting is that in verse 21, we find the "great sea giants". The term used there in Hebrew, literally means large reptiles. In modern Hebrew it has come to mean crocodiles, the descendants of these large reptiles, dinosaurs.
The first account of man is found in Chapter 1, and it says that man was made in G-d's image, or that he, or what was later to become homo sapiens, could think, and reason, to rule over the other animals. Later, around 974 generations before Adam, or about 25,000 years ago (The beginning of the Neolithic Age) man became complete as we know him/us today, homo sapiens. This man had evolved, or was formed from the dust of the ground, but was lacking the spiritual aspect until G-d breathed into him the breath of life...A soul, thus creating Adam Rishon, the first complete man. In Jewish tradition this happened on Rosh HaShanah, 5771 years ago, or 3,761 B.C.E.
And G-d took the man and placed him in the Garden of Eden... and it's been down hill and uphill from there... Up next: The beginning of the end of man the hunter-gatherer, agriculture, or we just thought that we knew better than G-d, the existence of other people (Adam and Eve weren't alone folks!) and the original industrial revolution.