@Prince709, that's a useful example, since most of the time the -n seems so arbitrary, confusing, unnecessary and inefficient. (I've seen some sentences that place a -j and -n on the end of almost every word in the sentence.)
Here's another example:
Kion iliaj ursoj manĝas? = What do their bears eat?
At first glance, I would have assumed that the -n should also be added to "iliaj".
Iliaj ursoj is what is doing the action - in this case eating. Kio is a question word and in this sentence it's asking what the bears are eating - it's the object of the sentence, it's what the verb is happening to, which is why it takes the accusative case. It isn't arbitrary, though it might feel strange if you don't speak other languages which consistently use an accusative case.
We do this all the time with pronouns in English without even thinking about it. He loves her, but she loves him. In Esperanto, the -n is used to mark the her/him equivalents.
In English, when we are talking about regular nouns, there's no difference (or at least I can't think of an example where there is a difference...), but oftentimes if you swap a noun for the equivalent pronoun, it will become more obvious.
For example, with the bears, we would say "what are they eating", not "what are them eating". Adding the accusative -n onto the end of iliaj would be like using them instead of they. The bears are not being eaten, they're the ones doing the eating, so they stay in the nominative case.
The major difference is that in Esperanto, the question word takes the accusative in the question if the answer will be in the accusative. Kion iliaj ursoj mangxas? Iliaj ursoj mangxas tion - 'their bears eat that'. Because the bears are doing the eating and the 'that' is being eaten, the bears stay in the nominative (the basic form in which you've learned the word) and the 'that' is marked as being in the accusative case.
FWIW, trust me when I say getting the hang of this in Esperanto will give you a leg up if you go on to learn another language with cases. There's only one and it's absolutely regular, with no grammatical gender to worry about. My first ever exposure to cases was Russian - six cases and three grammatical genders, and often not particularly regular. Trust me, it could be worse... ;)
I can't reply to the post I wanted to, I believe because it's at the limit of how deeply replies can be nested.
However, in the post where you mention that "Correlatives are hard to learn in insolation", you say that all of them starting with nen- are negative, and all ending with -ie have to do with a location.
Every textbook I've ever seen does not divide the words at that spot.
The first halves are:
i- ti- ki- ĉi- neni-
And the second halves are:
-el -al -es -o -a -u -e
So, it is the ending -e which means a place. This is why ie means somewhere, not just naked "place" by itself without a beginning.
Correlatives are hard to learn in isolation, IMO - it's worth finding a table of the correlatives so you can see how they relate to each other, like all of them that start with nen have a negative meaning, and if it ends with ie it refers to a place. Then when you come across a word like nenie, you don't need to have come across it before to know it must mean nowhere.
Wow, the -n is neither arbitrary, unnecessary or inefficient. I'll grant that it is confusing to beginners.
The -n marks the direct object and the adjectives that describe the direct object. Definitely not arbitrary! If in the sentence above you changed iliaj to iliajn, it would still be grammatically correct, but it would mean something quiet different.
Kion iliajn ursoj manĝas, asks what thing which belongs to a group of others is being eaten by bears.
Kion iliaj ursoj manĝas, asks what is being eaten by bears that belong to some group of others.
Very big difference. The lack of -n on iliaj means that iliaj must describe the ursoj. If it were iliajn with the -n that would mean it must describe the kion, the thing eaten.
If the answer to "what" should be in the nominative case, it's "kio". If the answer to "what" should be in the accusative case, it's "kion".
What do their bears eat --> Their bears eat what --> Their bears eat honey.
Since "honey" is the direct object of "eat", you need "kion".
What is his name --> His name is what --> His name is Adamo.
Since "estas" is a stative verb and thus does not take an object, you need "kio".