Audio is still being added, but there is quite a bit now. More will be added over time.
When you are in Duolingo, look carefully at the bottom of all tall straight letters. There is a curl at the bottom of the l (lowercase L) that is not present at the bottom of the I (uppercase i). In Klingon, L is always lowercase (l) and i is always uppercase (I).
The Klingon l is pronounced exactly as in English. In English we have a few different ways to say the letter i, but the Klingon I is always pronounced like in "it" and never like in "taxi" or "lite".