Click on the diagrams to see them better.  They represent the two most common types of radon systems. Sub-slab and sub-membrane ventilation.  Sub slab ventilation is used when there is an existing concrete floor.  A sub-membrane ventilation system is used when there is a dirt or stone floor as is the case with many crawlspaces.

                              This is sub slab ventilation.                             This is sub-membrane ventilation.