There are various resources for learning Klingon on the web, some better than others. I'm not going to recommend any because I've never found one I liked. This makes this list a bit random.
This KLI page explains the letters used to write Klingon:
http://www.kli.org/tlh/sounds.htmlThis is a KLI course, but it's much too short:
http://www.kli.org/study/postcourse.htmlThe Klingonska Akademien has lots of good reference materials, including a good dictionary, but no pages to learn from:
http://klingonska.org/Various wikis (which are always a work-in-progress):
http://mughom.wikia.com/wiki/QaH:A_Guide_to_Klingon - intended as a reference guide
http://en.wikiversity.org/wiki/Topic:Klingon - a very incomplete course
http://en.wikibooks.org/wiki/Klingon - another reference that has been started and never completed
http://en.wikipedia.org/wiki/Klingon_language - mainly background information and history
Pages from ter'eS:
http://teresh.tdonnelly.org/index.htmlThe Klingon academy has a module on the language, again not very complete:
http://www.academy.step-into.de/moodle/That should keep you busy for a while...