I usually do this when I want to use a new font:
Open Synaptic and search for the font. Maybe it's already packed for easy
installation from the repositories.
If the font is not available from Synaptic, I download it from the Web.
If I need the font to be available only for myself, I put it in my user
directory, inside the hidden ".font" directory (use Ctrl+H in Nautilus file
manager to hide/unhide).
If I need the font to be available system-wide (for all users), I do as
onpon4 and andrew suggested.
NOTE: and remember fonts also have licenses. I assume you're using Trisquel
because you care about freedom. So make sure the font you want to use is a
free cultural work
