Please could "New Word" dropdowns have more information!
As a native English speaker, I'm profoundly un-used to gendered grammar, and some of German's odder grammatical forms (Dative case, currently...) are also messing with my head.
It would be awesome if Duo's "New Word" dropdowns & the Vocabulary section afterwards had short notes explaining usage quickly, and more grammar notes generally.
After getting yet another exercise wrong because of not yet understanding "unser/useren/userem/etc/etc/etc" I'm feeling like Duo's current biggest weakness is it's lack of explanatory & supporting material. Sure, there's lots of other websites out there, but it would be awesome to have Duo-native explanatory material built right in!
Sounds like you're struggling with adjective endings, which are indeed tough until you master them. I picked up a great functional way of thinking about them from another user's comment, pasted below:
"Easier way to know adjective endings (my teacher side is coming out)! I have 3 rules for being able to add (or recognize) the correct ending when an adjective precedes the noun.
-Big 3 get an -e (der, die, das) der alte Mann, das kleine Kind, die schöne Frau
-Changin' gets -en (plural and case changes) den alten Mann (accusative), der schönen Frau (dative), die kleinen Kinder (plural)
-No 'the'? Adjective takes over (no 'der' word or just an 'ein-word') Kaltes Wetter gefällt mir nicht (das Wetter). Ein guter Mann ist schwer zu finden (der Mann).
Now the only tricky part is knowing which 'the' word your noun has :)"
Some added notes:
ein- words are: ein, mein, dein, sein, ihr, unser, euer, Ihr; "unser" is the root, which is confusing.
You do have to know what the gender of words are to get this right; IMO most people learn those with an outside program. I use an app called Ankidroid, which is open-source and available on most platforms (I use it on Ubuntu and Android).
I think it's difficult to include this in a word explanation, since some grammatical concepts are very complex. But I agree that there should be a grammar section somewhere on this site where the lesson can link to. There are so many good explanations and examples in the comments, someone should strat to harvest them and bake them into a good grammar reference.