Structure API is work in progress. You will find that some of the packages are documented less than others, and some are not documented yet.
We're constantly working on the API improvements and documentation and will make the javadocs and other parts of the documentation more complete with every release.
You can download javadocs from the Maven repositories into your IDE.
Check out information about Structure API Versions to select the correct API artifact, and you can also download Javadoc JARs there.