Hello, welcome and congratulations!
A GNU/Linux distro is basically a collection of packages. You'll need to
install some that contain Greek support.
There are many ways to do so, probably the most intuitive being the Synaptic
package manager.
I guess these packages might be useful for you. (from
http://packages.trisquel.info/search?keywords=greek&searchon=all&suite=belenos§ion=all)
abrowser-locale-el (if you use abrowser, believe this is default web browser)
icecat-locale-el (if you use icecat web browser)
icedove-l10n-el (if you use icedove email)
language-pack-gnome-el
libreoffice-help-el
libreoffice-l10n-el
xfonts-efont-unicode
xfonts-efont-unicode-ib
fonts-gfs-artemisia
fonts-gfs-bodoni-classic
fonts-gfs-didot
fonts-gfs-didot-classic
Besides installing those packages, you can change the keyboard layout in
System settings. (or whatever it's called in Trisquel 7)
My mother uses Trisquel, so you'll do just fine! :)
