Opening a port on WNDR3700

I am clueless on how to open a port on my WNDR3700. I need to open up port 6631. I went into my router setup and looked at "Configuring Port Forwarding to Local Servers" and at "Port Forwarding/Port Triggering". I did try the last one by entering in a range around that port but it didn't work. Should I be using Port Forwarding and if so where do I get the "Server IP Address"? Any help would be much appreciated.