Learn Hardcore Indonesian: Kami berlari tiga kilometer di taman.

So this sentence is talking about a group that doesn’t include the listener.
If the speaker wants to include the listener (“you and I ran…”), they would say:

Kita berlari tiga kilometer di taman.

Does this sentence mean “we ran” (past) or “we are running” (present)? Where is the tense?

Indonesian verbs usually do not change for tense.
Berlari can mean run / are running / ran / will run, depending on context.

Kami berlari tiga kilometer di taman could be:

We ran three kilometers in the park (past), or
We are running three kilometers in the park (present planned distance), or
We will run three kilometers in the park (future, in the right context)

To make the time clearer, Indonesians add time words:

Kemarin kami berlari tiga kilometer di taman.
Yesterday we ran three kilometers in the park.
Sekarang kami berlari tiga kilometer di taman.
Now we are running three kilometers in the park.
Besok kami akan berlari tiga kilometer di taman.
Tomorrow we will run three kilometers in the park.

What’s the difference between lari and berlari? Why use berlari here?

Lari is the basic root meaning “run”.
Berlari is formed with the prefix ber-, which often turns roots into intransitive verbs (verbs that don’t take a direct object).

lari – run (can be noun-like or verb-like; very common in speech)
berlari – to run (more clearly a verb; slightly more formal or neutral)

Both are correct here:

Kami lari tiga kilometer di taman. (more casual)
Kami berlari tiga kilometer di taman. (neutral / slightly more formal)

The meaning is essentially the same: We ran three kilometers in the park.

Can I say Kami lari tiga kilometer di taman instead? Is it still correct?

Yes, it’s correct and very natural.

Kami lari tiga kilometer di taman.
Kami berlari tiga kilometer di taman.

Both mean the same thing.
Lari sounds a bit more casual/spoken; berlari feels a bit more careful or formal, but both are standard.

Why is it tiga kilometer and not tiga kilometers? Where is the plural?

Indonesian usually does not mark plural with -s like English.

tiga buku = three book(s)
lima orang = five person/people
tiga kilometer = three kilometer(s)

The number tiga already shows that it’s plural, so the noun kilometer stays in its basic form. There’s no need to add anything for plural.

In English we say “ran for three kilometers”. Why is there no word like “for” before tiga kilometer?

Indonesian doesn’t need a preposition like for in this pattern.
You simply put the verb + distance:

berlari tiga kilometer = run (for) three kilometers
berenang dua ratus meter = swim (for) 200 meters
berjalan sepuluh kilometer = walk (for) ten kilometers

Adding untuk (kami berlari *untuk tiga kilometer*) sounds unnatural in this context.
So the natural form is exactly:

Kami berlari tiga kilometer di taman.

What exactly does di mean in di taman? Is it “in” or “at”?

Di is a general location preposition. It usually translates as “in,” “at,” or sometimes “on”, depending on context.

di taman = in/at the park
di rumah = at home / in the house
di sekolah = at school
di meja = on the table

So di taman could be understood as in the park or at the park; English has to choose one, but Indonesian doesn’t need to.

Why is there no word for “the” in di taman? How do you say “in the park” vs “in a park”?

Indonesian has no articles like “the” or “a/an”.

taman can mean a park or the park
di taman can mean in a park or in the park

The difference is understood from context, not from a word like “the”. If context is clear (for example, everyone knows which park you mean), di taman will be understood as in the park.

Does taman mean only “park,” or can it also mean “garden”?

Taman can mean:

“park” – public area, like a city park
“garden” – landscaped garden, decorative area, often with plants/flowers

Examples:

taman kota = city park
taman bunga = flower garden
taman rumah = house garden / yard

In Kami berlari tiga kilometer di taman, context (running three kilometers) strongly suggests a park, not a small private garden.

Is the word order fixed? Can I move di taman to the beginning or end?

Indonesian word order is somewhat flexible, but the basic neutral order here is:

Subject – Verb – Distance – Place
Kami berlari tiga kilometer di taman.

You can move di taman for emphasis or style:

Di taman kami berlari tiga kilometer.
In the park, we ran three kilometers. (emphasis on “in the park”)

Putting tiga kilometer before the verb (e.g., Kami tiga kilometer berlari di taman) sounds unnatural.
So keep the number phrase after the verb, but the place phrase di taman can move a bit.

How would I say it in the future or with a clearer “right now” meaning?

Base sentence:

Kami berlari tiga kilometer di taman.

To make the time clearer:

Future:
Besok kami akan berlari tiga kilometer di taman.
Tomorrow we will run three kilometers in the park.
Right now / currently:
Sekarang kami sedang berlari tiga kilometer di taman.
Right now we are running three kilometers in the park.
Habitual:
Setiap pagi kami berlari tiga kilometer di taman.
Every morning we run three kilometers in the park.

Is there a playful or repeated form like berlari-lari? Would that work here?

Yes, Indonesian often uses reduplication (repeating a word) for certain nuances.

berlari-lari suggests running around, running playfully, repeatedly, or here and there.

Examples:

Anak-anak berlari-lari di taman.
The children are running around in the park.

In your sentence, Kami berlari-lari tiga kilometer di taman sounds odd, because three kilometers suggests a purposeful distance, not playful running around.
So for a measured run, stick with:

Kami berlari tiga kilometer di taman.

How do you pronounce Kami berlari tiga kilometer di taman?

Rough pronunciation (syllables separated with dots; stressed syllable in CAPS):

Ka.mi – KAH-mee
ber.la.ri – bər-LAH-ree (the e in ber- like the a in “sofa”)
ti.ga – TEE-gah
ki.lo.me.ter – commonly ki-lo-ME-ter in Indonesian
di – dee
ta.man – TAH-man

Spoken smoothly:

KAH-mee bər-LAH-ree TEE-gah ki-lo-ME-ter dee TAH-man.