Adding the detector to the provisioning group will get the port listed as a service on a nodes particular interface. But to get it "monitored" you also need to add a matching poller. Here is a sample for generic DNS port 53 test.
provision group detector within the detectors section or via UI as Pete indicated:
<detector name="TCP-DNS-53" class="org.opennms.netmgt.provision.detector.simple.TcpDetector">
<parameter key="port" value="53"/>
</detector>
Matching poller-configuration.xml to get it monitored. i.e. events if the node stops responding to the port.
<!-- within the services section -->
<service name="TCP-DNS-53" interval="300000" user-defined="false" status="on">
<parameter key="retry" value="3"/>
<parameter key="timeout" value="3000"/>
<parameter key="port" value="53"/>
<parameter key="banner" value="*"/>
</service>
Then a monitor definition near the bottom.
<monitor service="TCP-DNS-53" class-name="org.opennms.netmgt.poller.monitors.TcpMonitor"/>
The detector, service names and monitor service all have to be identical.