The solution must lie in AirPort Utility (in your Utilities folder under the Applications folder).
This is from AirPort Utility help:
Direct network traffic to a specific computer on your network
To ensure that requests are properly routed to your web, AppleShare, or FTP server, or to a specific computer on your network, you need to establish a permanent IP address for the server or computer and provide inbound port mapping information to the AirPort Base Station or AirPort Time Capsule.
To use port mapping, you must configure TCP/IP manually on the computer whose ports you are mapping.
Thank you for the response. Here is the issue when I go to that configuration there is a drop down that wants you to choose a service, that would be fine if I knew what the service was. Let me try to explain a little further. The device I am trying to set up is a ethernet bridge from Nexia Home Automation which is part of Schlage Lock Company owned by Ingersoll-Rand. I called thier support and they told me I just need to open port 8879 on my router, which in this case is the TC. Here is a link to the Nexia product.
In order to set this thing up you have to create an account at www.mynexia.com and then it promps you to put the MAC address of the device into a web page to discover the device and then configure it. Well in my case I get the "three flashing green lights" on the device since from the web page it does not discover the device over my network. Which I am thinking is that why I need to enable this port.
Now on the Airport Utility when you go to the network tab the two items listed there are DHCP Reservations and Port Settings. I assume when youn say port mapping you mean settings. I click the + and then under description there is a drop down with options, you just can type in something, but then the options are Public UDP and TCP ports and private ones then it wants a private IP address. How do I know what IP the Time Capsule gave the Nexia bridge? What is the way to identify how to set this up?