What’s the difference between the Old Testament and the New Testament?
The Old Testament covers the beginning of God’s creation up until 400 years before the birth of Jesus Christ. This includes the creation of the heavens and the earth, the forming of man from the dust of the ground and God breathing into him the breath of life, the first lineages of mankind, the worldwide flood and Noah’s ark, the dispersion of people at the tower of Babel , and the calling of the patriarch Abraham (Genesis); the deliverance of the Hebrews from Egypt the giving of the law of Moses (Exodus thru Deuteronomy); their journey to and the establishing of their nation of Israel; their history from conquest of Israel to their disobedience of God’s Law and eventual captivity by Assyria and Babylon; and finally, the return of the Jews from captivity to their own land, howbeit from that time forward they remained under the jurisdiction of other ruling nations (covered in the remaining books of the Old Testament).
The New Testament covers the birth, life, death, resurrection and ascension of Jesus Christ (known as the four Gospels), the birth of the original apostolic church, how the apostles and church leaders evangelized the then-known world by preaching the Gospel and what was required to obey the gospel (covered in the book of Acts), 21 letters that were written to all these established churches on how to live a godly life that is pleasing to God and gains His blessing and favor (the epistles), and the final prophetic book depicting the end of all things (the book of Revelation).
I should note one other obvious and significant difference. The Old Testament was written in Hebrew and the New Testament was written in Greek.