I've noticed that the example sentences given for practice don't provide the tanwiin for case endings (though the TTS does say them, how correctly, I'm not sure). Is this for ease of learning so that we don't need to worry about those? Also, can someone give a brief on how they work?
Tanwiin or Nunation, can be considered at some point the "indefinite marker" for the word. Now, Nunation can be considered as an operation (and probably in ancient times it was a mere nasalization and not fully pronounced "N" sound). Why "operation"? Because it comes in 3 flavors coinciding with the short vowels (a, i, u) - when nunation is applied to those, they become (aN, iN, uN). I'm not sure how they are applied in this course on Duolingo, but it is probably as you said, for easy learning (and maybe they will provide lessons about those in a later skill). I'm not doing the exercises for Arabic myself as I'm a native speaker.
The sign for Tanwin coincidence, again, with the short vowel they represent; It can be either a double Dhamma (called Tanwin bil Dham) [-uN] (ُـُـُ) which is typically drawn as one symbol (ـٌ) [sorry i know the font is too small and it's a struggle for everyone],
double Fath^a (called Tanwin bil Fath^) ( ـً ) and that's [-aN], and finally a double kasrah (called Tanwin bel Kasr) ( ـٍ ) [-iN].
As to which to be used and in what situation, this is a grammatical lesson on its own
Ah, I thought tanwiin referred to the placement of regular short vowels on a word. So it refers specifically to the -an, -in, -un, interesting.
Mistake on my part there then, my intent was to ask which case endings (i.e. the fatHah, Dammah, kasrah or their tanwiin counterparts placed at the end of a word) indicated which case. I believe that is what you alluded to at the end of your post, though.
Ah, in that case it is a grammatical question. I don't wanna go deep here because things can get tricky even for a native like me (I was a failure at school really when it comes to Arabic grammar) but here are the simplest of cases for a singular regular noun (masculine or feminine) - not including exceptions and special cases:
- Nominal sentence (a sentence starting with a noun and does not need any verbs to be complete):
a. Mubtada' (nominal subject): -U(n)
b. Khabar (nominal predicate): -U(n)
- Verbal sentences (sentences starting with a verb, and includes a subject or a donor of the verb "Fá3il" and an object "Maf3úl bihi").
a. Subject (Fá3il): -U(n).
b. Object (Maf3úl bihi): -A(n).
As you can see, I didn't include the verb here because, well, it's a verb and not a noun and it has a bit of different considerations than nouns. I put (n) after the vowel to refer to the Tanwin in case of the noun here is indefinite. This is the basic - But the tree has many branches out there and the story might get long a bit :)