This setting is used to change the port where BitTorrent listens for incoming connections. If you are behind a router with network address translation (NAT), BitTorrent will attempt to configure your router's port mappings via UPnP or NAT-PMP. If your router is not capable of mapping ports automatically, you may need to configure port forwarding manually on your router. If your device has a public IP address (i.e. is not subject to NAT), you may need to change this setting if the default port is blocked by a firewall.
When set to "Automatic", BitTorrent automatically moderates its use of your Internet connection to avoid disrupting other applications and users. To impose a strict cap on BitTorrent's use of your connection, you may manually set the maximum rates at which BitTorrent will download, upload, and seed.
By default BitTorrent will seed a fully-downloaded torrent until you remove it. There are two alternative seeding policies that you may set. Seeding can be stopped automatically when the ratio of uploaded to download bytes reaches a threshold that you set. Or, seeding can be stopped automatically after a set number of minutes.