Adam and Eve live in the Garden of Eden. A beautiful place that God Created for them. They live with few rules, they cannot eat out of the Tree of Knowledge of Good and Bad.
One day, a serpent comes up to Eve and tells her that she should eat off of the tree, but she tells the serpent that God told her to not eat off of that tree.
The serpent then tells her that the tree will give her power that God has. Eve still refuses, but then the serpent tells her that God doesn't want her to eat out of the tree because then they will have the same amount of power.
with that, the serpent gives Eve an apple which she eats a bite out of. She then goes to Adam and tries to give him the apple. He asks her where she got it, and she tells him.
She repeats what the serpent told her. Adam is a little baffled but he takes the apple, thinking that it will give him the same power as God. He takes a bite out of the apple and hears God speak to them. The two run and hide in the bushes.
God asks where they are and Adam tells them what happened. God gets angry and tells them they are not allowed to go back to the garden and tells the serpent that he will have to slither on his stomach for the rest of his life. Adam, Eve, and the serpent run, and the serpent pecks at their heels. This is how Original Sin was formed.