According to Moses, God made the flood waters go away little by little, and after 150 days, the water finally went down enough. This made the earth dry once again so that people and animals could live on it.
Genesis 8:3: And the waters returned from off the earth continually: and after the end of the hundred and fifty days the waters were abated. [continually: Heb. in going and returning]
Genesis 7:24 states that the waters prevailed upon the earth for 150 days, whereas Genesis 8:3 implies the waters began to decrease gradually after the rains ended until the ark rested.
Genesis 7:24: And the waters prevailed upon the earth an hundred and fifty days.