I think based on the case the word is in, changes its' ending. For example, we've so far learnt 3 forms of Riña: nominative, plural, and accusative. Nominative is just the standard case (Riña), plural is girls (Riñi), and accusative is a peculiar case that isn't used in English but in High Valyrian, the accusative case of Riña is Riñe.
There's some exceptions to the rule, but the following all follow the same rule:
Nominative: Vala - Man Abra - Woman Taoba - Boy Rina - Girl
Plural Vali - Men Abri - Women Taobi - Boys Rini - Girls
Accusative Vale - Man Abre - Woman Taobe - Boy Rine - Girl
I hope that's starting to make sense. I had to restart the entire course and write down all the sentences and translations on a notepad to help me understand it. Here's some more information from the tips and notes. I hope it's useful - let me know :)
This is from Basics 2:
The second case you're going to learn about in this lesson is called the accusative case. The accusative case is used with the object of the sentence. For example, in the English sentence "The man sees the woman", "the man" is the subject (the seer), and would take the nominative case in Valyrian. "The woman", on the other hand, is the object (the seeee), and would take the accusative case. In High Valyrian, rather than word order, the form of the noun is what tells you who does what to whom. In this case, ābra "woman" changes its ending from its usual -a to -e. There are several different strategies for forming the accusative case, so pay attention to each new form you see.
Oh, thank you for your answer ! I think I am starting to understand the thing.. But I keep asking myself : Why "Rina urnen" would not work ?
This is because "the girl" is the object, and she takes then the accusative case ?
Yes.. I think that's it.. Thank you, it's indeed making more sense ! :D
Glad I could help! Keep going over these because it is complicated. It's not just the nouns that change as well, but verbs, adjectives, etc all change depending on things. Try writing down the sentences and translations and it should start making sense. High Valyrian is definitely a hard language.