How do I type extra fonts in Ubuntu 10.4?

Cyrillic, Greek, Arabic, Kanji, etc..
I’ve installed a few packages (live tex, etc..) but I need someone to tell me a simple way to actually use these fonts for instance whilst typing a message on facebook, or simply writing a note on my desktop.
I know of at least one way to interchange between font categories : by pressing shift. I think I saw this being done on windows XP. but it’s not important to me, just need an easy and quick to shift between fonts groups.