The Bible as a whole is of great importance to the Christian believer. The New Testament, in particular.
The Old Testament tells us prophecy of the coming of Jesus. It tells us of who God is, what God did, what He expected from His people "the Israelites", how he wants to be worshiped and tons of wisdom for each of us as individuals. It is a biography of His people, the things they did wrong and what they did right. The Old Testament is full of the law of God and how the people could not live by His holy law.
The New Testament is the biography of Jesus. It tells us of his birth and his death, burial and resurrection. There is direction in Acts on how to be saved and the epistles tell us how to stay saved. Revelation tells us what to expect when we die from this earth.
For today the New Testament is the place for all new believers to start learning. But once you get your feet wet you need to study more and delve into the wonderful knowledge of the Old Testament so you can be well rounded in the knowledge of God.