Kind of! Thank you. Actually it's pretty confusing without some kind of systematic explanation of Hindi grammar. I haven't spent enough time with the section notes yet, so maybe a full explanation of the oblique case/postpositions etc is in the section notes and I just haven't found it yet?
Yeah I don't think there's much grammar explanation around. From what I saw, Duolingo tries to focus on raw pattern learning rather than grammar learning. The idea is that if you try to learn Hindi through it's grammar, it will look rather easy, but you won't be able to speak it fluently. Like imagine trying to read Devanagari with a table on the side for the letters, you could decypher it, but not like how you're reading Latin characters. At the same time, I think grammar could come as a posterior explanation of what you observed in a lesson, and reinforce what you had heuristically learnt with the true heuristics.
Anyway, my advice is try to figure it out without thinking too much, when you can't seem to understand ask around here, and if you come to a point you really really need grammar, I can only recommend hindilanguage.info, but I'd rather advice you to look at it at a later stage and to refresh memories briefly if you haven't practiced in a long time.
I'd even add, if you can, try to do Duolingo just listening/speaking. Basically when it says the sentence in Hindi, use Google voice to type in the answer in English, and when it shows the sentence in English (well read it, it doesn't say it out loud), use Google voice to type in Hindi (you can select "use your own keyboard"). Also when it asks you to pick a sentence between three, speak out loud how you would say it and compare with the answers. The idea is the more you train to vocalise/hear, the better you'll get, a language is spoken before written. Also, you can do extra exercise with the sentences you're being given by putting it plural, indirect speech, changing the tense, etc. "मेरे पिता जी को सेब बहुत पसंद है" my dad loves apples, "उसके पिता को सेब बहुत पसंद है" his dad loves apples, etc. That would help you with a big problem of Duolingo: it tries to translate. You would need to set your brain in one language only to build the most efficiently your brain around it, so thinking about it from a Hindi sentence and transforming it keeps you in that language.