The Passover was in the time of Moses and Pharaoh and Aaron. God tells Moses and Aaron to be ready and to tell the people to get some lambs and to put it on their doorframe. If they did not, everyone's firstborn would have to die. Because God was going to go to Egypt at midnight, and if the people didn't have the lamb's on the door, their firstborn child will die. God says that it was the same for human as for animals. Just all the firstborns would die. But if you had the lamb's on the door then you and your family will not be harmed. Moses told the elders of Egypt this and that they will go to a ceremony and when their children ask them what the ceremony is all about they will tell them that it is the Passover sacrifice to the Lord, who passed over the houses of the Israelites in Egypt and spared our homes when he struck down the Egyptians. Everyone was to get a lamb or goat and take care of it for fourteen days. On the fourteenth day they were to slaughter it and roast it's head, legs, and it's insides. They were not to leave any till morning; if some were left till morning, they would have to have burned it. They were supposed to eat it with their cloaked tucked into their belts, and their sandals on their feet, and their staff in their hand. On that night the Lord will pass through Egypt and strike down every firstborn-both men and animals- and He would bring judgment on all the gods of Egypt. God wants everyone to remember that day from generations to come. Everyone is to eat and celebrate the Feast of Unleavened Bread. .
When God came through the towns at midnight that night he killed every firstborn there was that did not have lamb's on the doorframe. God even killed the pharaoh's son. And when Pharaoh found out that his son was he wailed till all of Egypt could hear him.