I wouldn't actually call it a Reference in its common meaning. However it can be used as a reference as well. In addition to guiding you through the
IDE features (with the help of a sample project), the book also provides you with useful tips, shows workarounds basing on real-world use-cases, etc.
It is obviously better to have IntelliJ IDEA installed when reading the book, but even without that, one would get an impression of what this tool really is.