To search, select a Criteria Type and a Criteria.  For searches using Criteria Types: Classification, Characteristic, or Reason for Regulation, select the Criteria from the drop down box.  For searches using Criteria Type: List Name, use the Filter button to narrow the choices in the text box.  

You must select either the "Add Expression AND" or the "Add Expression OR" button before selecting the Search button or before selecting a new Criteria Type and Criteria.  "Add Expression AND" creates an intersection between two search criteria.  "Add Expression OR" creates a union between two search criteria.