Below is a sample pom.xml illustrating how to use it.
<plugin>
<groupId>org.apache.maven.doxia</groupId>
<artifactId>doxia-book-maven-plugin</artifactId>
<version>1.3-SNAPSHOT</version>
<executions>
<execution>
<phase>pre-site</phase>
<goals>
<goal>render-books</goal>
</goals>
</execution>
</executions>
<configuration>
<books>
<book>
<directory>src/books/example-book</directory>
<descriptor>src/books/example-book.xml</descriptor>
<formats>
<format>
<id>latex</id>
</format>
<format>
<id>xdoc</id>
</format>
<format>
<id>pdf</id>
</format>
<format>
<id>rtf</id>
</format>
</formats>
</book>
</books>
</configuration>
</plugin>
See also the sample given on the main Doxia site.