In part 1, Basics, you looked at types in a superficial manner. Part 2 discusses the Julia type system in greater detail by building up various examples, such as a recurring rocket example, that demonstrate how the type system works and what benefits it offers.
This part introduces what makes Julia special. The greater depth of coverage of the type system in this part also allows me to cover how functions and methods work in Julia. In particular, it allows a proper explanation of multiple dispatch, which is the killer feature in Julia. Multiple dispatch is at the heart of what makes Julia such an expressive and high-performance language, despite being dynamically typed.