This page describes the new Libgda's report component, as it has been changed from the 3.0.x versions. The reason of that change (even though it breaks API/ABI compatibility) is that the report component did not work in 3.0.x versions and needed to be fixed.
The report component is essentially a report engine which operates on any XML file containing some special <gda_report_...> nodes which, when the engine is run, are transformed into information (can run a SELECT query, can evaluate expressions, etc).
It's up to the user to provide a template file which the engine transforms. This operating mode allows to create very flexible reports based on the needs of the user: for example for very precise page layout and for a PDF output, the XML dialect of choice will probably be RML, whereas for a more standard approach, a DocBook XML template will be better.
More information (including examples) can be found in the samples/Report directory of Libgda's sources, or from the SVN repository.
The current documentation is available from this page