The most widely supported theory for the creation of the universe is the Big Bang Theory. It states that the universe was created about 13.7 billion years ago from a singularity (a very, very hot point with an infinitely small volume and infinitely large density) and it has been expanding ever since (so getting less dense and less hot). Click here for a timeline since the Big Bang.
The 4 main arguments supporting this theory are sometimes called the 4 pillars of the Big Bang Theory, click here for an article regarding those core arguments. Also, this video regarding 'Olbers' Paradox' might be of interest to you too, it's actually one of the most blatantly obvious arguments for the Big Bang Theory.
Of course, there are alternate theories, but at the moment this is the most widely supported one.