You can access a Port using the usual Alf notation for a Property. Sending a Signal or calling an Operation on the Port (consistent with the Port's type) then makes an invocation through the Port and across any Connector attached to the Port. That is, the Alf invocation is mapped into an invocation action whose onPort property is set to the target Port.
The Alf language requires that the type of a property that is the target of a Signal send have a Signal Reception for the Signal being sent. Therefore, in order to send a Signal through a Port, the type of the Port must have a Signal Reception for the Signal.