Learn Hardcore Indonesian: Mereka menyalakan lampu taman sebelum pesta dimulai. - They turn on the garden lights before the party starts.

mereka is the third-person plural pronoun “they.” It functions as the subject of the verb menyalakan, so the sentence literally means “They turned on the garden lights …”

What is the root word of menyalakan, and how do the prefix and suffix work?

The base (root) is nyala (meaning “light” or “to be lit”). To form menyalakan we:

Add the causative suffix -kan to get nyalakan (“cause to light up”).
Attach the verb‐forming prefix meN- to nyalakan.
Due to regular spelling rules, meN- + nyalakan becomes menyalakan, meaning “to turn on (something).”

Why is menyalakan used here instead of menyala?

menyala is an intransitive verb meaning “to light up” or “to be on” (the lamp lights itself).
menyalakan is transitive/causative (“to make something light up”), so you need an object (here, lampu taman).

What does lampu taman mean, and why isn’t there a preposition like di?

lampu taman is a compound noun:

lampu = “light” or “lamp”
taman = “garden”
Together they mean “garden lights.”
No preposition is needed in a noun‐noun compound. If you wanted to say “the lights in the garden” (emphasizing location), you could say lampu di taman.

What is the role of sebelum, and how does it affect the clause pesta dimulai?

sebelum is a subordinating conjunction meaning “before.” It introduces a time clause. Everything after sebelum is treated as a dependent clause, here pesta dimulai (“the party is started” / “the party begins”).

Why is pesta dimulai in the passive voice? Could you use pesta mulai instead?

dimulai is the passive form of mulai. Indonesian often uses passive di- to describe events without mentioning an agent.
Yes, you can also say pesta mulai (“the party starts”) using the intransitive verb mulai. The nuance is slight:
• pesta dimulai ⇒ “the party is begun” (focus on the event happening)
• pesta mulai ⇒ “the party starts” (focus on the party itself starting)

Can you change the word order by putting the time clause first? Is a comma needed?

Yes. You can say:
Sebelum pesta dimulai, mereka menyalakan lampu taman.
Putting sebelum-clause first is common. A comma is optional but often added in writing to mark the clause boundary.

Is it possible to omit mereka and still understand who is doing the action?

Yes. Indonesian frequently drops subject pronouns when the context is clear. You could say:
Menyalakan lampu taman sebelum pesta dimulai.
—but including mereka makes it explicit that “they” (some group) did the turning‐on.