[Trisquel-users] Re : Installing Tor -

[magicbanana]

Just to expand on this laconic URL. Here is how you add the correct line to  
your /etc/apt/sources.list file (assuming you use Trisquel 5.5 Brigantia):
sudo echo 'deb http://deb.torproject.org/torproject.org oneiric main' >>  
/etc/apt/sources.list

Then pursue with adding the gpg key as explained on this page.