According to Genesis, God created the heavens and Earth over six days.
Genesis 1 presents creation as an ordered sequence. Light appears on the first day; the sky separates waters on the second; dry land and vegetation appear on the third. The fourth day introduces the sun, moon, and stars, followed by sea creatures and birds on the fifth day. Land animals and humanity are created on the sixth day.
Genesis 2 describes the seventh day as a time when God rested, blessed it, and made it holy. This is why the answer is six days rather than seven: the seventh day is portrayed as the completion and rest following creation.
The Genesis account is often discussed alongside other ancient Near Eastern creation traditions, but its six-day structure is especially influential in Jewish and Christian ideas about the week and Sabbath. The question asks specifically about the creation work described in Genesis, not the length of the entire creation week.