Genesis 6:17-18, 22

For behold, I, even I, will bring a flood of waters on the earth, to destroy all life under the heavens in which there is the breath and spirit of life; everything that is on the land shall die. But I will establish My covenant (solemn promise, formal agreement) with you; and you shall come into the ark—you and your [three] sons and your wife, and your sons’ wives with you.

So Noah did this; according to all that God commanded him, that is what he did.