To generate the static html pages, Poormans is using the Apache-Velocity-Engine, a template engine. The mode of operations of those template engines is always the same. A template is merged with some content. This content is provided by 'context objects', common java pojos provided Poormans. Please refer this part of the javadoc to get an overview about these objects. To understand how the Apache-Velocity-Engine is working refer this documentation.
To get an idea how this in working in Poormans, take a close look to the source code of the templates and makros of the demo site.