Learn Hardcore Indonesian: Saya mempelajari lagu pop baru di perpustakaan setiap sore. - I learn a new pop song in the library every afternoon.

belajar is more general and intransitive: it means “to learn” or “to study” in a broad sense.
mempelajari is derived from the same root but uses the prefix mem- and suffix -i to make it transitive, emphasizing the act of studying something thoroughly. In other words, you belajar in general, but you mempelajari a specific object (e.g., a subject, a skill, or in this case, a song).

What do the affixes mem- and -i do in mempelajari?

mem- (a form of the meN- prefix) changes the base verb pelajar (study/learner) into an active verb.
-i marks the verb as transitive, signalling that it takes a direct object.
Together, mem-…-i turns a root into “to study (something).” Without -i, mempelajari would lose its direct-object focus.

Why is it lagu pop baru and not lagu baru pop?

lagu pop is treated as a compound noun meaning “pop song.”
baru (“new”) then modifies the entire compound.
So structurally it’s: [noun + genre] + [adjective].

Can I say lagu baru to mean “new song” without mentioning the genre?

Yes. lagu baru simply means “new song.” Omitting pop broadens the meaning to any kind of song.

Why is there no article before perpustakaan? How would I say “a library”?

Indonesian doesn’t have definite/indefinite articles like a, an, or the. Context makes it clear whether you mean one, several, or all libraries.
If you specifically want “a library,” you can add sebuah or suatu before it: sebuah perpustakaan.

Why is the preposition di used in di perpustakaan? Could I use ke perpustakaan instead?

di indicates a static location (“at/in the library”).
ke indicates movement toward a place (“to the library”).
Since the sentence describes where the studying happens (static), you use di.

Where can the time phrase setiap sore go? Can I start the sentence with it?

Yes. Time expressions in Indonesian are flexible. You can say:

How do we express plural for lagu? Is lagu-lagu required?

Indonesian generally marks plurality through context, not by adding an “s.”
lagu can mean one song or many songs, depending on context.
If you want to emphasize “multiple songs,” you can say lagu-lagu pop baru (“new pop songs”), but it’s not mandatory here.

How do you pronounce perpustakaan?

Break it into syllables: per-pus-ta-kaan

“per” as in “purr”
“pus” as in “poos”
“ta” short “tah”
“kaan” with a long “ahn”
Stress typically falls on the penultimate syllable: per-pus-TA-kaan.