You seem confused about something. In all TCP 'conversations' there is
a source and a destination port. The destination port is set by
service. For example, smtp 'listens' on port 25, and ssh 'listens' on
port 22. Stations initiating the conversation use a random unused port.
For example, a mail server sending you an e-mail will open port 4502
locally to talk to your port 25. This is why a firewall has both source
and destination ports. You almost never control the source port, so it
is usually set to any. The destination port is the service you want.