If you’re at all serious about learning Klingon, you need to be on the Klingon Language Institute site—if for no other reason, to access the list of words that have been added to the language since the publication of The Klingon Dictionary. The best way to get any practice at the language or feedback is to join the tlhIngan Hol Email Discussion Group.
You’ll still need to learn the grammar and vocabulary from The Klingon Dictionary, which is under copyright.