Reading through my book, the lesson I was on was articles and it went through the indefinite articles "ein" "eine" and "ein" (again) which mean "a" or "an" and which gender they are used for, I wish it also taught me about "einen" "einem" and "einer" and when they are used aswell as Duolingo uses those also and I have no idea when they would be used and how. Same with "den" and "dem" Duolingo also uses those for "the" and I have no idea of how or when they would be used. I guess as I go along I'll learn, but at the level I'm at it is all so confusing.