Creatio ex nihilo is the teaching that God created the universe out of nothing. The idea is compatible with the Big Bang theory as often presented: the universe started with a singularity of infinite density; before the Bang occured, there was no "matter" or "stuff." With the Bang, symmetry breaking occured, and matter came into existence.
Gen 1 does not teach creatio ex nihilo. It does not narrate the creation of an inchoate earth, the waters of the abyss, the darkness which covered the abyss, or the wind that hovered over said waters; all of the above pre-exist the first creative fiat the narrator recounts: "Let there be light!" (Gen 1:2-3). It does not explain the existence of divine beings apart from God and apart from creation, those included in the "Let us make man" of Gen 1:26. But Gen 1 does teach what creatio ex nihilo teaches: that the universe is, without remainder, the product of a sovereign infinite singularity, referred to as "God." In Gen 1, there is no place for a power in heaven or earth comparable to that of the sole deity described throughout as the Creator and Lord of heaven and earth.