The Dataset Selector shows all datasets available for the data source chosen in the Data Source Selector. PostGIS were selected at this example but the behavior is the same to all data source types. See how to access this interface here.

To select one or more datasets just check the corresponding box and press Select button.

Before the selection, it is possible to see a  Map Preview or Data Preview of each dataset (check the box). Then,  click over the dataset name on the list (or check the dataset corresponding box) and a preview will be showed. 

After pressing Select  all datasets  will appear at the TerraView main window on the Layer explorer.