Yes! You should set up port forwarding to get the fastest possible transfer speeds on BT, unless you have a UPnP-enabled router, in which case port forwarding is done dynamically when necessary.
By default, BT uses TCP ports 6881-6999, although different clients may be set up to use different ports. Many of them will even allow you to specify which port(s) they should use within their settings panels.
In BT terminology, a "seed" is a peer that has already finished downloading the whole file, but is continuing to upload it to other peers requesting the same file. As you might expect, there needs to be at least one "seed" for every torrent shared. Conversely, "leechers" are peers who are downloading and uploading pieces of the same file simultaneously. So when downloading any file, you typically start off as a leecher and become a seed when the download completes, unless you close off your BT client after it's done.