In the biblical account found in the book of Exodus, God calls Moses while he is tending to his father-in-law's flock of sheep on Mount Horeb. Moses sees a burning bush that is not consumed by the flames, and when he approaches it, God speaks to him from the bush. God identifies himself as the God of Abraham, Isaac, and Jacob, and tells Moses that he has heard the cries of the Israelites in Egypt and has chosen Moses to lead them out of slavery.
God instructs Moses to go to Pharaoh and demand the release of the Israelites, promising to be with him and to perform miracles to demonstrate his power. Moses initially hesitates and expresses doubt in his ability to carry out this task, but God reassures him and provides him with signs to perform as proof of his divine authority.
Ultimately, Moses accepts God's call and goes to Egypt to confront Pharaoh, leading the Israelites out of bondage and towards the Promised Land. This call of Moses by God is seen as a pivotal moment in the history of the Israelites and is a central theme in the story of the Exodus.