So, in the instant before the universe exploded outwards(Exploded isn't the right word, but bear with me, it's simpler to use it), all the matter in the universe was collected in a single point, a singularity; A place where matter is packed so tightly that it's density is infinite and it's volume is zero. This also gives it an infinite gravitational field, which in turn makes time go infinitely slow - it doesn't move at all, but "stops". Also, at this point, matter and energy is packed so densely, and the pressure and temperature are so high, that the four fundamental forces - That is, electromagnetism, the strong nuclear force, the weak nuclear force, and the gravitational force, are combined, to form a sort of "super force", which scientists today cannot even guess would actually do on a subatomic scale. Anyway, this also means that time, which is dependant on gravitation, also ceases to exist as we know it, since there is no gravitational force. As such, when the big bang "happens", and matter starts exploding outwards, time is formed in the sense that we know it, and matter existed before time. What happens after the big bang is not really important, but the thing is, that using what we've seen here, there is no reason in asking what came before the big bang, as matter, and all the things in the universe always existed, as long as time itself existed. Also, there is of course no reason in asking what came before time, since "before" implies that we are traveling in a continuum of time, which is nonexistent. I hope this cleared things up.