So "yaj" in this sentence would be more like "is understood by" instead of "understands"?
No, not at all.
What Mara does is yaj. She understands.
The person she understands is Torg.
Since Klingon sentences have the object first, then the verb, then the subject, we have torgh yaj mara, Mara understands Torg.
Consider also a compound sentence such as torgh yaj mara 'ej Sop mara "Mara understands Torg and Mara eats."
It does not mean "Torg is understood by Mara and is eaten by Mara" -- the sentence doesn't say that Torg is eaten, only that Mara eats (something).
The subject is really "Mara understands" and "Mara eats"; Torg is not the subject in any way, shape or form.
Using an English passive sentence to translate a Klingon active sentence can be a helpful tool for beginning to understand the Klingon word order, but it is not an accurate translation. The point of the English passive construction is to allow you to stress the object or focus on the object by putting it before the verb in the subject position. In Klingon this is just the normal way of saying things and doesn't give any special stress or focus.
This method of translating Klingon also breaks down when there is no object - you can't use it to translate a sentence like wa'leS jIqet ("Yesteday I ran") or jIQuch jIH ("I am happy.") You also can't use it for the Klingon copular construction like juHwIjDaq jIHtaH ("I am at my home.")
So you can't allow yourself to start thinking of the passive construction as a proper way to translate Klingon sentences, but it might be a nice trick to practice thinking in Klingon word order.
I feel for you. We've all gone through the difficulties of those beginning stages at some point. The problem is that it is so different from English it requires a type of re-wiring of the brain to learn it. In addition, since many users don't know about the Tips & Notes, they find it even harder to just figure out from the example sentences. If you haven't been reading the Tips & Notes, you will probably find them to be extremely helpful. Please scroll through this entire sentence discussion to find the big post with instructions how to find those Tips & Notes.
No. Please don't read the sentence backwards. Instead, try to get used to hearing/reading the information in a different order. It will be be difficult at first, but as you get used to it you will find it easier. If you have not been reading the Tips & Notes, I would like to ask that you review those.
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). When you click on a Skill, it will expand to reveal a large Start button and a large 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 any Skills, we are happy to answer your questions, but many of your questions will probably already be answered in the Tips & Notes.
Not to disagree, but my Father and I are learning at the same time. We have repeatedly failed this one because it in fact does not accept "understands" "understood" and "will understand" ... it is the sole purpose of my comment. Somebody needs to check the programming. We had the same problem with "English" and "Federation Standard" with "DIvI' Hol" ... it does not always accept both