Feeding data sources using Spoon into Pentaho Report

Hello,
I'm new to Pentaho and the product looks very promising so far. However, I'm running into some difficulties setting up some basic transformations and I'm probably just not understanding something.

What I'm trying to do is create a report template using the Report Design application, and have the data sources be fed in via a transformation. Is this possible? I think I'm supposed to use the 'external' data source for this and then create custom parameters that link with the data source being fed in. Am I on the right track? Is this possible?

Some of the documentation seems lacking in this area.

Thanks for any input