Port Mapping

NAT port mapping only works if your network router connected to internet supports UPNP or PMP API. You can read more about it in WIKI article here: http://en.wikipedia.org/wiki/Universal_Plug_and_Play.

Even if router does not support it, you can still manually open port. You can find a manual for your router on this web site: http://portforward.com/english/routers/port_forwarding/
Besides you don’t absolutely have to open ports, download would work without that. The only problem is that other peers would not be able to initiate connection to your device, but once connection is established from your side everything would work just fine.

Torrent RT has a built in feature to enable port mapping if your router supports this. You can change it from settings page.