When Moses got older and became an adult, he came across one of Pharaohs guards beating a Hebrew Slave. Moses confronted the man and they got into an altercation. They started fighting and Moses killed the man.
Moses had to run away to the dessert and leave town after Pharaoh heard about the altercation and wanted Moses sent to death.
One day when Moses was in the mountains, he came across a burning bush. It was God trying to reach out to him about the Hebrews being held as slaves.
Moses went to Pharaohs castle to tell him about what God had told him, but Pharaoh laughed and told him to get lost.
When Moses returned to God and told him what had happened, it made God upset. This gave God the idea of giving Moses the ability of using magic in different ways upon Pharaoh
After days and days of Pharaoh disobeying God's orders, God made the choice of killing Pharaohs first born. This made Pharaoh saddened and forced him to give up the Hebrew slaves.