Basic use means that you configure the plugin from the POM. However, it doesn't run automatically, but on demand:
mvn apache-rat:check
To achieve that, a section like the following needs to be added to your POM:
<build>
<plugins>
...
<plugin>
<groupId>org.apache.rat</groupId>
<artifactId>apache-rat-plugin</artifactId>
<version>0.12</version>
</plugin>
...
</plugins>
</build>