The usual answer: 66 books
If you pick up a typical Protestant Bible, it has 66 books. The Old Testament has 39 books, beginning with Genesis and ending with Malachi. The New Testament has 27, beginning with Matthew and ending with Revelation.
These books were written by many people across centuries, in different settings. Moses wrote about God forming Israel. David brought his prayers and grief to God in the Psalms. Prophets such as Isaiah spoke into troubled national life. Then the Gospels tell the story of Jesus, and letters from Paul, Peter, James, John and others guide the early churches.
Though it is a library rather than one single-volume work, Christians receive these writings as a connected witness to God's work in the world. Jesus himself spoke of the Scriptures as pointing towards him (Luke 24:27).
And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.
Why some Bibles have more
Catholic Bibles include 73 books. Along with the 66 found in Protestant Bibles, they include seven further Old Testament books: Tobit, Judith, Wisdom, Sirach, Baruch, 1 Maccabees and 2 Maccabees. They also contain longer portions of Esther and Daniel.
These writings are often called the Deuterocanonical books, meaning ‘second canon’ or ‘second collection of recognised writings’. Protestant Christians often call them the Apocrypha. They are ancient Jewish books, and many readers find them historically and spiritually valuable, especially for understanding the period before Jesus' birth.
Christians have disagreed, with care and conviction, about whether these books belong in the Old Testament canon, the collection regarded as Scripture. Catholic and Orthodox churches receive them as Scripture. Most Protestants do not place them on the same level as the 66 books, though some Protestant editions print them separately.
The New Testament is shared
Whatever Bible tradition you read, the New Testament contains the same 27 books. There are four Gospels, one account of the early church in Acts, 21 letters, and Revelation. They centre on Jesus' life, death and resurrection, then show how his followers carried his message into the Roman world.
The early Christians paid close attention to the teaching passed on by Jesus' apostles. Paul urged Timothy to hold firmly to what he had learned from trustworthy teachers (2 Timothy 3:14). The church gradually recognised the books that faithfully carried this apostolic witness.
But continue thou in the things which thou hast learned and hast been assured of, knowing of whom thou hast learned them;
A good place to begin
The number can feel a little overwhelming. Don't try to master all 66 at once. Start with one Gospel, such as Mark or Luke, and read it slowly. Notice what Jesus does, whom he welcomes, and what he says about God.
Then perhaps read Acts to see what happened next, or Psalms to find words for prayer. The Bible's books have different styles, including history, poetry, wisdom, prophecy, biography and letters. Reading each book on its own terms helps its message become clearer.
Scripture is meant to be heard, pondered and lived, not merely counted. As Paul writes, it equips God's people for a life shaped by what is good (2 Timothy 3:16-17).
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works.