Select one of the draw tools (polygon, rectangle, circle), draw a shape and click the search link that pops up.
Import an existing GIS area (currently supported formats: Well Known Text (WKT) POLYGON shape)
To search with other spatial file formats (shapefile, KML, etc.), please use the Spatial Portal - via the "Add to Map" ➜ "Areas" menu.
Copy & paste a WKT POLYGON string and click "Add to map":