In the garden of Eden, Adam and Eve could eat freely of any tree in the garden except the tree of the knowledge of good and evil.
Satan came to Eve and questioned what God had said and tempted her with eating the fruit from the tree of the knowledge of good and evil.
Eve took the fruit and ate it and gave some to Adam to eat too. When they did this they knew they had done wrong and felt ashamed. They made coverings with leaves to hide themselves and when God came to see them they hid from Him.
Adam and Eve were kicked out the garden of Eden, there were curses on the land and illness and disease and death entered the world. They could no longer walk with God in the garden like they used to be able to do. They were separated from God because of their sin.
But God made a promise that He would provide a Saviour who would restore the broken relationship between us and God by taking the punishment for the sin men and women.