I see that you are doing Scandinavian languages. The Y in Finnish is pretty similar to those found in them. Start with the long I found in kiitos (or the English word "sea"). Then pout like a proud puffer fish. Do the same again, but keep the sound short. If you're a perfectionist, Y is pronounced just a tad closer to the teeth than I. :)
Zzzzz... is right. To pronounce an "y", it is better to begin with "ea" in sea (the Finnish "ii), than with "oo" in moon (Finnish "uu"). And thank you for your tremendous work with this Duolingo course! Your advice in Tips how to reflect English articles with the word order in Finnish was also fine. Kiitos paljon suurenmoisesta työstä!