The source code is organized in such a way that each chapter has its own folder, named by convention as Chapter 1, An Introduction to Scala 2.13, to Chapter 15, Project 2 - Building Microservices with Lagom. You can experiment with examples by navigating to the appropriate folder and starting SBT. It is recommended to occasionally issue the git pull command for the cloned repository to get recent updates and bug fixes, shown as follows:

Each chapter has its own configuration files, project/build.properties and build.sbt. The former configure the version of the SBT to be used, the latter the required version of Scala and other dependencies. The SBT will download and cache all configured versions as required. This is why we don't need a separate installation of Scala.