For example, if you with to create a binding connection between a constraint parameter symbol and a part property symbol when using the smart manipulator (context popups), go FROM the constraint parameter symbol TO the part property symbol.
(When binding to/from a value property it does not matter, the smart manipulator context popup menu only offers a BindingConnector from a value property symbol.)
BTW: Regular Connectors may be accessible (depending on your environment preferences) in any case also under the sidebar menus.