The Old Testament either refers to the 39 canonical books of the Hebrew Scriptures written prior to the coming of Christ, or to the time period before Christ came, when God's people belonged to the nation of Israel. A better translation for "Old Testament" would probably be "Old Covenant", while some also prefer "First Testament."
The Bible is divided up into sections that help us understand what we are reading. Just like when you read the newspaper that has a sports section, a financial section, the front page stories, and all the rest; the Bible is divided up into helpful sections.
The Law (Torah):
Includes Genesis through Deuteronomy.
Mostly stories/narratives that run in chronological order
Includes Joshua-Esther and Lamentations
Includes Job-Song of Songs
Divided into two sections based on length (Major=longer, Minor = shorter):
Major Prophets: Isaiah-Daniel
Minor Prophets: Hosea-Malachi