Features, eg attributes and operations, cannot exist outside an element. This is true in the project browser and in diagrams; it is part of the UML standard.
What EA does when you drag an operation onto the empty space of a diagram, since obviously you don't want the operation all on its own in the diagram, is try to create the nearest non-feature equivalent of an operation, which is an action, specifically a 'call operation' action. These belong in activity diagrams, so read up on those for details on how actions and action pins work.
Regarding creating connectors between elements and operations, you can't. Again, this is down to UML: operations Do Not Have connectors.
What Q describes is an EA feature to make it appear as if you can draw connectors to features, which you can use if appropriate. Remember, however, that the ends of the connector, as stored in the database, are still the two elements. The fact that one end is linked to a feature is not actually syntactically valid, so it's stored in one of the undocumented additional data columns which you'll have to dig through and decode.
So there are ways and ways, but it does depend on what relationship you want to represent. My BPMN is a bit rusty, but aren't activities callable elements?
/Uffe
