Obviously, Christians believe that God created the universe. Interestingly, however, the New Testament states that God the Son somehow had a special part to play in the creation process:
John 1:3: Through Him all things were made; without Him nothing was made that has been made.
Note that the Bible doesn't go into details about how this was achieved. I am not interested in arguing with neo-atheists such as Richard Dawkins (whose philosophy of science is remarkable naive, by the way).
Another important point is that God the Son is seen, not just as creating the universe, but also as continually sustaining the existence of the universe:
Heb 1:3: The Son is the radiance of God's glory and the exact representation of his being, sustaining all things by his powerful word.
In this sense, Christianity can be contrasted with "Deism", the idea that God set the universe running and then left it to its own devices.