A port type is a named set of abstract operations and the abstract messages involved. Each operation refers to an input message and output messages. A port type is referenced by a binding object. Each binding references exactly one port type. Since each port refers to exactly one binding, each port has exactly one port type.
You can create a port type by right clicking in any blank area in the design workspace and selecting Add PortType. As a convenience you can also add a port type via a binding. This allows you to create a port type and modify the binding to reference the new port type in one action.
You can either create a new port type for your binding, or reuse an existing one.