Ok. So here you are, on your shiny GNU/Linux and dont know how these "torrents"  work.
Ive been testing a LOT of bittorrent clients and now im gonna guide you through my absolute favorite
one, just read ahead and you will know all abaut downloading uploading and setting some basic
settings.
rtorrent, http://libtorrent.rakshasa.no/
(screenshot på guiet)
So if you used MPLayer before this wont be to hard for you, as the usage with the keyboard is
somewhat the same.
Installation, if you are using a modern distribution with some kind of package managment you can
probably use it to install rtorrent if you are using ubuntu like me just do sudo apt-get install
rtorrent, but often repos are outdated so if you want the new version you need to compile it
yourself. for that you need gcc make and some other related utilities, sudo-apt get install
build-essential got that for me in ubuntu. then you need the source to compile, do it like this
wget http://libtorrent.rakshasa.no/downloads/libtorrent-0.10.1.tar.gz
http://libtorrent.rakshasa.no/downloads/rtorrent-0.6.1.tar.gz
unzip the files.
tar xzfv libtorrent-0.10.1.tar.gz
tar xzfv rtorrent-0.6.1.tar.gz
compile rtorrent/libtorrent
cd libtorrent-0.10.1/ ./configure make sudo make install
cd rtorrent-0.6.1/ ./configure make sudo make install
If you choose to compile, then the procedure is same in every GNU/Linux distrobution
If you used the package managment in your distro or compiled it yourself you have it installed by now.

So here comes the usage and litte quirks
To start the torrent type rtorrent filename.torrent in a console
Then you can navigate the client with upp/down/left right, as you se there are some basic information you can acces,
for ex go to the files and press space to get either OFF HIGH or NORMAL priority and by doing such you can select
wich files you want and priority.