I have a book on beginning Polish that I reference while going through this course. Duolingo is great for practicing and internalizing grammar structures which traditional classroom style teaching often neglects, but I too often struggle with understanding the intricacies of the case system. The book I have has very "light-weight" grammar explanations that are often too cryptic. I would definitely recommend keeping a Polish grammar book on hand while studying. I too will be searching out a more robust book on Polish grammar to accompany my study.
These discussion pages are often very helpful, but I often get lost in the explanations due to little familiarity with the vocabulary used to describe the case system (personal? non-personal? instrumental? accusative?...but no one is being accused of anything in this sentence!) Having never learned a language using grammar case before, the explanations are no less challenging than the target language material.
Beyond the target language material, if feasible, it would be wonderful to have some exercises dealing with the case system itself, while including the vocabulary used to describe it.
The hardest part of this language so far is the noun and adjective endings based on the usage of the word. I've been trying to do separate research on them. It would be really nest if this course also quizzed you on if a word is masculine feminine or neutral, the Polish cases, and the endings specifically in certain situations as well.
It may still not be consistent in terms of accepted answers, but generally 'to be wearing' is not a proper translation of 'nosić'.
This is one of the few examples when Polish shows a difference between Present Simple and Present Continuous. "nosić" is "to wear" (and also "to carry), while "to be wearing" is "mieć na sobie". Which is unfortunately not taught in the current version of the course.
potem, it's one word.
Well, "czarny" as any adjective has to match the grammatical gender of the noun it describes. "płaszcz" is masculine, "spodnie" are 'not masculine-personal plural'.
The notion of being inanimate is important only if you have masculine singular noun in Accusative. So yeah, it's important with "płaszcz". Płaszcz is inanimate, so its Accusative form is identical to Nominative. Thefore "Mam czarny płaszcz". If the noun was masculine singular animate, the form would be identical to Genitive. "Mam czarnego psa" (I have a black dog). That's the only situation when the difference between animate/inanimate matters.