1. First, a quick definition of terms (our glossary has more complete definitions). A resource is one of the objects you want to find by navigating a facet map. In this case, the resources are bottles of wine -- specifically, bottles of wine pirated from wine.com and compiled into a sample dataset for this demo.
A facet is a certain classifiable characteristic of the resource -- a way to classify something. Here we have "Varietal", "Region", and "Price", which are different ways for different people to classify wines. The different facets allow each of those people to focus on what they want.
A heading is an attribute that each bottle of wine might have. Varietals, e.g. Merlot or Champagne, are headings here, as are such appellations as Tuscany or Sonoma Valley. Plenty of other attributes could be headings, like "12% alcohol", or "medium-bodied", or "wine I drank in high school", but we'd have to define more facets to support them.