Exodus is a history book in the Bible's Old Testament. And Exodus is also a law book.
The people called Hebrews were slaves in Egypt. God sent Moses to free them (Exodus 3). The people in Egypt did not want to free these slaves. But God caused many terrible troubles in Egypt. These troubles forced the people in Egypt to free their Hebrew slaves. So, the Hebrew people left Egypt.
God promised the land called Israel to the Hebrew people. But the journey to Israel was through a desert. God did many wonderful things to help the people through the desert. God provided water (Exodus 17) and food (Exodus 16).
Moses met God at a mountain called Sinai (Exodus 19). There, God gave the law to Moses (Exodus chapters 20-30). Moses made a special tent where the priests would serve God (Exodus chapters 35-40).