D.A. Carson and Douglas Moo’s Introduction to the New Testament is a top-notch textbook, which I’ve found very helpful. If you want it essentially boiled down to its conclusions, then take a look at Andy Naselli’s condensed version, Introducing the New Testament: A Short Guide to Its History and Message. It’s short (176 pp.) and you can get it for under $10.
In addition to introductions on studying the NT, the synoptic gospels (Matthew, Mark, and Luke), the NT letters, and Paul, each chapter answers the following questions about each book of the NT:
1. Content: What is the book about?
2. Author: Who wrote the book?
3. Genre: What style of literature is used?
4. Date: When was the book written?
5. Place: Where was this book written?
6. Audience: To whom was this book written?
7. Purpose: Why was this book written?
8. Contributions: What does the book contribute to our understanding of the faith?
You can read below the whole chapter on Romans: