Here's a quick synopsis of the story of the Hebrews leaving Egypt and (eventually) settling in the Promised Land (the land of Canaan which is now modern day Israel/Palestine)
1) Moses convinces the Pharaoh of Egypt to free the Hebrews from their bondage as slaves
2) In order to escape before the Pharaoh changes his mind, the Hebrews leave Egypt and enter the Sinai wilderness on their way to the Promised Land
3) They stop at the base of Mount Sinai while Moses ascends the mountain
3) At the top of the mountain, God (Yahweh) appears to Moses and gives him the Judaic Law inscribed on two tablets of stone. This law is generally depicted as the "Ten Commandments" but actually the law is much more extensive than just the commandments known as the Ten Commandments
4) However, because the Hebrews worship idols and ignore Yahweh's commandments, they are punished by having to wander in the Sinai wilderness for 40 years (long enough for all the adults to die) before they can reach the Promised Land
"biblical proportions" means "gigantic scale" e.g. a flood that covers the whole earth, disasters that destroy entire cities, etc.