SMTP servers listen for connections on port 25. Echo servers listen on port 7. Discard servers listen on port 9. Not all services have a well-known port. For example, NFS allows the ports to be discovered at runtime.
Protocols Loosely speaking, a protocol defines how two hosts talk to each other.
In networking a protocol defines what is and is not acceptable for one participant in a conversation to say to the other at a given moment in time. For example the daytime protocol, specified in RFC 867, says that the client connects to the server on port 13. The server then tells the client the current time in a human readable format and then closes the connection. On the other hand the time protocol, specified in RFC 868, specifies a binary representation for the time that's legible to computers. Both daytime and time send the same information.