The most likely reasons for wanting to build Spring Layout from source would be:
If you don't already have Maven installed you should download and setup Maven as per the Maven website
The project structure in Spring Layout is to some degree based around the Eclipse IDE. It should format correctly in eclipse straight out of SVN without the need to run the eclipse:eclipse goal.
To build Spring Layout and install it in your local maven repository for reference by other applications you should navigate to your Spring Layout project directory and run the "mvn source:jar install" goal. If you are doing this and configuring Spring Layout as a dependency in your project be sure to check that you are referencing a current version in your pom.xml.