Sometime after the creation of Adam and Eve on the sixth day of creation, see Genesis 1:26-31, they rebelled against God by eating the fruit of the tree of the knowledge of good and evil.
“So when the woman saw that the tree was good for food, that it was pleasant to the eyes, and a tree desirable to make one wise, she took of its fruit and ate. She also gave to her husband with her, and he ate.” Genesis 3:6.
When God confronted Adam and Eve after their sin in the Garden of Eden, see Genesis 3:1-24, He pronounced a series of curses and punishments; within this God made reference to the coming Christ who was to take away the sin of the world.