In those days, men lived a long time, but God told them even then that He would eventually set the limits on man's days at 120 years. Not too many people live to be 120 years old nowadays. God looked upon the earth, and behold, all flesh was corrupt. God then told Noah how to make the ark. He told him to put pitch on it.
Pitch is like tar.
It kept the ark sealed up. God also told Noah to make a window on top of the ark and a door on the side of it. The ark was to be three stories high. Then God told Noah what He was going to do. God was very serious.