It is believed that G-d oversaw the distress of the Jews who were working as slaves in Egypt, and sent numerous warnings to Pharaoh to stop the cruelty, but Pharaoh turned a blind eye. G-d then sent upon Egypt ten devastating plagues, destroying everything from livestock to crops.
At the stroke of midnight of 15 Nissan in the year 1313 BCE, G-d visited the last of the ten plagues on the Egyptians, killing all their firstborn. While doing so, G-d spared the Jewish people, “passing over” their homes—hence the name of the holiday. The Jews left in such a hurry that the bread they baked to eat during the exodus from Egypt did not have time to rise. We commemorate this haste by eating unleavened bread (matzah) during the holiday.
Pharaoh chased after the Jews, who found themselves trapped between Pharaoh's armies and the sea. G-d told Moses to raise his staff over the water; one of the miracles of this holiday occurred when the Red Sea then split to allow the Israelites to pass through, and then closed, drowning the pursuing Egyptians.
Six hundred thousand adult males, plus many more women and children, left Egypt on that day, and began the trek to Mount Sinai.
The story of Exodus is captured in the book called the Haggadah, which we read during the Passover seders each year to commemorate our freedom and liberation. Key words from the story appear on the Passover Bingo board game!