In the time when Noah was alive, he was the only man who does the right thing. All the people was just doing bad things which made God really angry.
God said he'll send a flood to the earth to destroy every living thing. God remembered Noah so He told Noah to build an ark and take his family also with animals. Noah did what God said to him.
The rain fell hard for 40 days and 40 nights. Water flooded the whole earth but the boat was safe.
A few months later, the other mountains can be seen. 40 days later, Noah released the raven to find out if there's dry land but the raven came back. After 7 days, he sent the dove out and came back with an olive leaf. After 1 week, he released the dove and didn't come back meaning there's dry land already.
Noah waited for 2 more months until the earth was dry. Finally, God told them to leave the boat. They all left the boat happily. Noah made an alter to make a sacrifice to God. God was pleased and He made a promise to Noah.
God promised that "Never again will all life be cut off by the waters of a flood; never again will there be a flood to destroy the earth." God made a rainbow as a sign of promise to Noah and his family.