The plugin will not be enabled by default. To enable it in the current project, go to “File→Settings...→google-java-format Settings” (or “IntelliJ IDEA→Preferences...→Other Settings→google-java-format Settings” on macOS) and check the “Enable google-java-format” checkbox.
To enable it by default in new projects, use “File→Other Settings→Default Settings...”.
google-java-format*all-deps.jar by running mvn install in the core directory.google-java-format.iml module to this project by doing File→New→Module from Existing Sources... and selecting the iml file.core/target/google-java-format*all-deps.jar file. IntelliJ will ask if you want to add it as a dependency to the google-java-format module. You do.