This is the post #19 of the Calvin's Institutes summary series, and is the summary of the whole Book I.
Calvin seems to focus on three things in Book I:
1) The doctrine of Scripture: The bible is the sure source of the knowledge of God.
2) The doctrine of God: The God of the bible is a triune God, who is one and only true God. And it is unlawful to make any images of God. (There is some discussion on the doctrine of man included.)
3) The doctrine of providence: God is sovereign over all things, directing both good and evil events, yet He is never guilty of evil and we are never without responsibility for what we do.
These are practical knowledge of God the Creator. With these doctrines, Christians can be assured that they can know God truly (because we have the bible), and we are given an amazing revelation of God who is utterly different to anything we could imagine (the triune God), and He loves and cares for us with His almighty power (providence of God), and so we are to be humble, thankful, patient, and confident throughout this life.