Genesis 3:1-7 - "Now the serpent was more crafty than any of the wild animal the Lord God had made. God said to the woman, 'Did God say you must not eat from any tree in the garden?' The woman replied, 'We may eat fruit from the trees in the garden, but God did say, 'you must not the the fruit that is in the middle of the garden and you must not touch it, or you will die.' 'You will not surely die,' the serpent says to the woman, 'for God knows that when you eat of it, your eyes will be opened and you will be like God, knowing good and evil'. When the woman saw that the fruit of the tree was good for food and pleasing to the eye and also desirable for gaining wisdom, she took some and ate it. She also gave some to her husband who was with her and he ate it. Then the eyes of both of them were opened and they realized they were naked so they sewed fig leaves together and made coverings for themselves."
I know that was a long passage, but it shows how sin came into the world. Let me give you some background on it. God had an angel named Lucifer. He was the most handsome of all the angels. He didn't like to be under God; he wanted to be God. So he, and some other angels, decided to make their own "group". That's when God named him Satan. Satan was using the serpent to make Eve sin. When she ate the fruit and made Adam eat it, their eyes opened (I think it means literally) and they saw that they were naked. They felt ashamed. That was when they first sinned. So, God didn't want sin to be in this world. Some people say, "God made everything, why did he make sin?" Don't blame God. And remember- when you sin, confess to God and repent by changing the way you think. Then that sin will be washed away by the blood of Jesus.