How long did it take for God to create the heavens and the earth? This question is rather simple. The Bible gives us the answer: 6 days. It's literally the first thing we read in the Bible. Genesis 1 gives us a beautiful overview of each of those 6 days and what God did in those 6 days. The beginning of Genesis 2 then describes the 7th day, on which God is said to have rested.
But to many Christians, this extremely simple concept seems extremely complex. When God says 6 days, did He really mean 6 days? Answer: We better hope so, for the sake of the weekend, because in the oh so famous 10 commandments, God literally bases the Sabbath day on the Creation week.
In Exodus 20:11, God tells the Jews that He created the heavens and the earth, resting on the 7th day, therefore the 7th day is blessed and hallowed. God worked for 6 days and rested on the 7th, therefore the Jews were to work for 6 days and rest on the 7th.
This concept still echoes through history to us today. A year is based on the earth's orbit around the sun, and a month is based on the phases of the moon, but from where does the concept of a week come? There are no celestial bodies that give us a 7 day time period. The concept of a week comes from the first week in history: The week in which the heavens, the earth, and all that is in them, were created by the Lord.
Without the 6 days of creation, and the 7th day on which God rested, there would be no 6 days of work, nor a 7th day of rest, for the Jews, nor would there be a period of 7 days called a week even in secular culture. Thus, the doctrine of Creation is not only easy to understand, but a correct understanding of it is an essential foundation to another important doctrine.