The descendants of Adam and Eve multiplied.
Many people turned away from obeying God and did wicked things. This evil that people did against each other made God very sad, because it made it impossible for them to enjoy the loving and happy lives that God had intended. God decided to stop the evildoers.
There was one man who did good and loved God. His name was Noah. God asked Noah to build a big boat, and then for him and his wife, his three sons and their wives, and representatives of land animals and birds to board the boat to live there. God told Noah to also store enough food to last for many days as a great flood was about to cover the earth.
It took Noah many, many years of work to build this very large boat called the ark. He and his family had a big job to do in order to get it ready before the flood came.
You can read this story and what happened to Noah and his family in Genesis chapters 6–8.