Learn Hardcore Indonesian: Guru menilai tugas akhir kami di perpustakaan. - The teacher assesses our final assignment in the library.

If you really want to emphasize one teacher in a neutral, countable way, you can say seorang guru (= a teacher / one teacher), but it’s not required here. Context usually tells you whether English should use a or the.

What is the subject, verb, and object in this sentence?

The basic structure is standard Indonesian S–V–O:

Guru = subject (the teacher)
menilai = verb (evaluates / evaluated / is evaluating)
tugas akhir kami = object (our final assignment)

Then di perpustakaan is an adverbial phrase showing location (in the library).

Does menilai mean is evaluating, evaluated, or will evaluate?

menilai itself has no tense; it just means to evaluate / to assess / to grade.
Indonesian usually does not mark past, present, or future on the verb. Context or time words clarify:

Kemarin guru menilai tugas akhir kami di perpustakaan.
= Yesterday the teacher evaluated our final assignment in the library.
Sekarang guru menilai tugas akhir kami di perpustakaan.
= Now the teacher is evaluating our final assignment in the library.
Besok guru akan menilai tugas akhir kami di perpustakaan.
= Tomorrow the teacher will evaluate our final assignment in the library.

Without any time word, the sentence can be understood as past, present, or a general/habitual action, depending on context.

What is the base form of menilai, and what does the prefix me- do?

The base form (root) is nilai, which can mean value, score, or grade.
The prefix meN- (here realized as me because the root starts with n) turns it into an active transitive verb: menilai = to evaluate / to assess / to grade (something).

So roughly:

nilai = value, score
menilai = to give a value/score → to assess/evaluate

What exactly does tugas akhir mean? Is it always final assignment?

Literally, tugas akhir is final task.

Usage depends on context:

In school or general contexts: often final assignment or final project.
In universities in Indonesia, tugas akhir can be a more substantial final project at the end of a program, sometimes similar to a thesis, although there are also specific terms like skripsi, tesis, disertasi.

So tugas akhir kami here is naturally understood as our final assignment / final project, but exact translation can vary with context.

Why is kami placed after tugas akhir, not before like in English (our final assignment)?

In Indonesian, possessive pronouns usually come after the noun, not before it.

tugas akhir kami = our final assignment
(literally: final assignment our)

Other examples:

buku saya = my book
rumah mereka = their house

So tugas akhir kami is the normal, correct order.

What is the difference between kami and kita, and why is kami used here?

Both kami and kita can mean we / us / our, but:

kami = we (excluding the listener)
kita = we (including the listener)

In tugas akhir kami, the teacher is talking about our final assignment, and the speaker is excluding the person being talked to (likely the teacher or someone else), not including them in the group that owns the assignment.

If the speaker wanted to include the listener, they would say:

tugas akhir kita = our (including you) final assignment

Could we say tugas akhir kita instead of tugas akhir kami? How would that change the meaning?

Yes, grammatically tugas akhir kita is fine, but the nuance changes:

tugas akhir kami = our final assignment (you, the listener, are not part of the group)
tugas akhir kita = our final assignment (you, the listener, are part of the group)

So you would use tugas akhir kita when you and the listener are both owners/authors of that assignment (for example, you and your classmates discussing your own group project together).

What does di mean in di perpustakaan, and how is it different from ke?

di is a preposition that indicates location: in / at / on.

di perpustakaan = in the library / at the library

ke indicates movement towards a place: to.

ke perpustakaan = to the library

So:

Guru menilai tugas akhir kami di perpustakaan.
= The teacher evaluates our final assignment in/at the library.
Guru pergi ke perpustakaan.
= The teacher goes to the library.

Does di perpustakaan describe where the teacher is, where the assignment belongs, or where the evaluating happens?

By default, di perpustakaan is understood as describing where the action happens:

menilai di perpustakaan = evaluates in the library

So the most natural reading is: The teacher evaluates our final assignment in the library.

Technically, it could also be interpreted as our final assignment (that is) in the library, but in normal usage, an adverbial location placed at the end like this is usually taken to modify the verb (the action), not the object’s identity.

Can we move di perpustakaan to another position in the sentence?

Yes, adverbials like di perpustakaan are relatively flexible. Common alternatives:

Di perpustakaan, guru menilai tugas akhir kami.
(Fronted for emphasis on the location.)
Guru di perpustakaan menilai tugas akhir kami.
This tends to sound like the teacher who is in the library evaluates our final assignment, because di perpustakaan now looks like it is describing guru.

The original Guru menilai tugas akhir kami di perpustakaan is the clearest neutral version.

How do we know if guru is singular or plural? Could it mean the teachers?

Indonesian nouns usually do not mark singular vs plural. guru can mean:

a teacher
the teacher
teachers (in general, or the teachers), depending on context.

If you want to emphasize plurality, you can use:

para guru = the teachers (group of teachers)
guru-guru = teachers (plural, often with a sense of many/various)

In your sentence, guru is most naturally understood as singular the teacher, unless context suggests otherwise.

Could we say seorang guru menilai tugas akhir kami di perpustakaan? What’s the difference?

Yes, you can say:

Seorang guru menilai tugas akhir kami di perpustakaan.

seorang literally means one person, and with a profession like guru, it functions like a / one:

seorang guru = a teacher / one teacher

The nuance:

guru menilai … = the teacher (assumed known from context) evaluates …
seorang guru menilai … = a (certain) teacher evaluates … (you introduce this person for the first time or don’t specify which teacher exactly)

Could we say tugas akhirnya instead of tugas akhir kami?

You could say tugas akhirnya, but it changes the structure and meaning:

tugas akhir kami = our final assignment (possessive pronoun kami = our)
tugas akhirnya = his/her/its/the final assignment or the final assignment (with -nya acting as a pronoun or a definite marker)

-nya is versatile; it can mean his/her/its, or act like a kind of the in some contexts.
In the original sentence, we specifically want our, so kami is the correct possessive pronoun.