The nouns do not have actual cases, but Klingon is a nominative-accusative language distinguished by word order with the object first (if there is one), then the verb, and then the subject. Also, the verbs are conjugated by means of verbal prefixes which indicate both object and subject and so the explicit object and subject can be elided and a conjugated verb may serve as a complete sentence.
Each verb has a prefix on it and the prefix indicates both the object and the subject. Many languages only conjugate for the subject, but Klingon uses the prefixes to conjugate for both object and subject. When there is no prefix it indicates that there is a third person subject (he/she/it/they) and either no object or a third person object (him/her/it/them). There is actually one specific third person combination that is not included in the null (i.e. absent) prefix (when the subject is plural and the object is singular the lu- prefix is used).
The basic word order in a Klingon sentence is described in the tips and notes for the very first lesson unit.
If you've read it before, you may want to refresh your memory by going back to the "Word order" section of https://www.duolingo.com/skill/kl/Useful-phrases/tips-and-notes .
If you haven't read them before, and particularly if you didn't even know that tips and notes exist:
Before you start a new lesson unit, go to the website https://www.duolingo.com/ and click on the unit symbol, then on the lightbulb icon in the little window that will appear when you do:
Tips and notes for Klingon are unfortunately not (yet) available in any of the mobile apps, so you will have to open the website in a browser to access them.
Inverted? You mean how Klingon uses the basic sentence structure of Object-Verb-Subject which is the opposite of English Subject-Verb-Object? Yes, I suppose one could call that "inverted". However, as you study the language you will find that not everything is in the reverse order from English, so it is better to learn Klingon word order than to think of it in reverse English order. A short paragraph about this is included in the Tips & Notes. If you have not read the Tips & Notes, I would like to suggest that you review those so we don’t have to continuously repeat the information that we have explained there.
If you are doing the course on iOS or Android, you cannot currently access the Tips & Notes through the app. To access the Tips & Notes, you will have to access the course using a web browser at https://www.duolingo.com/. You can still do it on your mobile device, but you will have to use the web browser instead of the app (or you can do it from a computer, which will be a little easier to read). When you click on a Skill, it will expand to reveal a Start button and a Tips button.
If you click on the Tips button it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes for the previous and current Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
I wish the programmers would just do away with all the reports except "my answer should be accepted", since they provide no detail about what the problem was, what platform was being used, or even what kind of exercise it was. And I also wish they would make the forums easier to find and use from the apps, so people could come here and explain the problems they encounter.
In English that is called a passive sentence and is often discouraged by English teachers who usually recommend an active sentence like, "Mara does not understand Torg." In fact, Klingon has no way to create a passive sentence like that and the typical way to translate it into Klingon is, torgh yajbe' mara. I suppose you could argue that your English suggestion should thus be accepted as a translation of this Klingon sentence. I don't like it as an English sentence and I don't even want to consider adding variations for passive versions of every sentence in this course. I will not be adding it as an accepted translation. However, I do commend you for noticing that the meaning is the same even though the grammatical structures are different.
You are confusing a few different topics here. "You are missed by me," is the English passive voice. On initial glance, many Klingon sentences can seem to match the word order of the English passive voice. In actuality, the Klingon sentences are active sentences, but the basic parts of the Klingon sentence are written in reverse order from their order in the English sentence. But not all Klingon sentences can be represented as English passive voice, so it is not a good idea to equate the two. You should work on training your brain (through practice and repitition) to hear the thing being acted upon (the object), then the action happening (the verb), then the one taking the action (the subject).