In the beginning, when God created the heavens and the earth, God also created Adam, a man. He gave him everything he could want including a helpmate.
But they were foolish. Eve, Adam's helpmate was tempted by satan, in the form of a serpent, to eat of the fruit of the tree of Knowledge of Good and Evil. God had told them that they were not to touch the tree. But satan told Eve that she would be like God if she would eat the fruit. (Unfortunately, what she didn't realize is that they were already like God. And God said, Let Us (Father, Son and Holy spirit) make mankind in Our image, after Our likeness.[Amplified Bible]
When Eve believed satan's lies, (because satan is the father of all lies), she ate of the fruit, and then offered it to Adam, who also ate of the fruit. They knew right away they had done something bad, and they hid from God.
Scripture References:
Genesis 1
Genesis 2
Genesis 3
Genesis 1
Genesis 2
Genesis 3