I am assuming you are on the Calculation Definitions tab of the workflow profile. In the Dependent Entities area you will see the list of Entities Assigned (see the Entity Assignment tab - double-click 1 or more Entities from the Unassigned Base Entities area. Those Entities now appear on the Calculation Definitions tab). The box that is in the screenshot you attached is used to filter the Dependent Entities - enter some text and then click the Filter button to the right.
