In the beginning God created the heavens and the earth.
This verse sums up all things that exists as having been created in the beginning by God.
The heavens and the earth did not always exist, they were created. God created them, but God was uncreated. God simply is what he is.
In the beginning indicates a starting point. I take this to mean the beginning of everything, including all spiritual creations, as well as physical. God is the origin, the source of the existence of the heavens and the earth. Though they have a point of beginning, God has none. He simply is.
The heavens and the earth are dependent for their created and sustained existence, but God is independent. If we were to say that God is dependent on something, he would depend on himself. He is self-existent. That is to say, God's existence depends on God. Another way to put it is to say that he is ultimate. He is the bottom line, so to speak.
God acted in creation. He performed a work. Power, which is the ability to do something, was exercised by him, through him, and for him.
Creation was ex nihilo, or from nothing. God, who is, made something to be that was not until he caused it to be.
In speaking of reality, God is the ultimate reality, for only he simply is. All reality besides him is from him and depends on him for it to be real. All reality is therefore God's reality. In looking at this verse, it seems that all dependent reality is contained in two levels:
1) the heavens
2) the earth
Both levels exist as creaturely, that is, they are created. There is a distinction of essence between the Creator on the one hand, and the created on the other. The Creator exists apart from and independent of the created, and the created exists from and dependent on the Creator. Nothing exists apart from God, though God exists apart from everything besides himself. Therefore God is holy, separate, different, wholly other than his works of creation.
On account of this doctrine, God is to be regarded by us as sovereign, that is, he is supreme and authoritative. We look to him for all that we are and can be.
The subject of science often enters into discussions about creation from Genesis chapter one. But we must keep in mind that science, which comes from a latin word meaning knowledge, is the study of the natural world through human observation. When we speak of a natural world, we are speaking of the creation that depends on God for its existence. When we speak of human observation, we are speaking of created beings capable of knowing things by virtue of their created existence. So when we talk about science, we are talking about creation and what we can know about it. Such things are only possible because God has made them so. That is why the person who wants to separate his knowledge of God from what he can know about nature, studying it independently from him and calling that 'science', is badly mistaken. We depend on God in order to do even that. Therefore we must acknowledge our dependence on God as our Creator and Sustainer in order to know anything at all as it should be known, and by doing so, honor and glorify him.
Note, a fuller treatment of epistemology cannot be treated here, nor can a refutation of atheism, other religious traditions, or an in depth study of what other ancient cultures thought about creation be dealt with here. Those are topics for another occasion. However, I should mention that this verse comes down to us as part of God's revelation of himself and his works to us, his creatures. God communicated the knowledge of himself and his act in creation in order that we might know something about it, and therefore the message of verse one of Genesis chapter one is dependent on God's revealing it, which we believe and confess he has done.