The purpose of this explanation is to give you a framework for better understanding the Bible on your first read-through, not to replace it like Spark’s Notes.
The Bible is a collection of books divided into the Old Testament and the New Testament. The thesis is the Gospel, which I’ve summarized as “All people sin, sinners go to Hell, believe in Jesus and be saved.” That’s the main takeaway of the whole collection, and I’d recommend Googling around for explanations of “the gospel” if you don’t already grok it. There’s a lot of interplay between the two book collections in the form of Old Testament prophecies predicting New Testament events and New Testament figures referring to events, prophecies, and laws in the Old Testament.
The Old Testament books describe God’s relationship with the Israelites, and the theme is obedience versus disobedience to a very explicit set of rules, ad nauseum. Story after story, it goes one of two ways: 1) the Israelites were obedient, so God rewarded them, and 2) the Israelites were disobedient, so God punished them. Since the rules were primarily intended to protect the Israelites from the consequences they didn’t understand, it’s easy to draw an analogy to parents trying to raise children.
The New Testament books describe Jesus’ relationship with the church, and the themes are forgiveness, salvation, and following the spirit of the law. Jesus summarizes the spirit of the law in only two commands: “The most important one…is this: ‘Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.’The second is this: ‘Love your neighbor as yourself.’ There is no commandment greater than these.” Christians are instructed to internalize these principles and act accordingly rather than merely following a rulebook.
Personally, I recommend reading the New Testament first because it’s shorter and more important, whereas the Old Testament is only important insofar as puts the New Testament into context. I don’t think it’s very important to stress out about which translation to use, anymore than you’d stress out about which translation of The Illiad to use. You can always sperg out about perfect accuracy later. For answers to questions regarding authenticity and such, I recommend carm.org.