Learn Hardcore Indonesian: Di kamar kosku, ada gorden biru dan tikar kecil di lantai. - In my boarding room, there is a blue curtain and a small mat on the floor.

kamar = room
kos = rented room / boarding house / dorm-style room (common in Indonesia for students or workers)
-ku = my (attached to a noun as a suffix)

So:

kamar kos = boarding-room
kamar kosku = my boarding-room / my rented room

The suffix -ku is an informal, attached form of aku (I), used for my:

buku (book) → bukuku (my book)
rumah (house) → rumahku (my house)

Could I say kamar kos saya instead of kamar kosku? Is there a difference?

Yes, you can say kamar kos saya, and it is correct.

Difference:

kamar kosku
- uses suffix -ku
- a bit more informal, often in speech, texting, casual writing
kamar kos saya
- uses separate pronoun saya
- more neutral and polite; fine in most situations

Meaning is the same: my boarding room.
In formal writing or talking to someone you don’t know well, kamar kos saya is safer.

What does ada mean here? Is it like is/are?

ada is best thought of as there is / there are.

In this sentence:

ada gorden biru dan tikar kecil
= there is a blue curtain and a small mat

Use ada to say something exists or is present in a place:

Di dapur ada meja. = In the kitchen, there is a table.
Di tas saya ada buku. = In my bag, there is a book.

Indonesian does not use ada as a general is/are between a subject and adjective:

Dia tinggi. (not Dia ada tinggi.) = He/She is tall.

Why isn’t there any word for a or the in gorden biru and tikar kecil?

Indonesian does not use articles like a/an or the.

So:

gorden biru can mean a blue curtain or the blue curtain, depending on context.
tikar kecil can mean a small mat or the small mat.

If you need to be more specific, you use context, demonstratives, or numbers:

gorden biru itu = that blue curtain / the blue curtain
tikar kecil ini = this small mat
satu gorden biru = one blue curtain

Why do the adjectives biru and kecil come after the nouns gorden and tikar?

In Indonesian, adjectives usually come after the noun.

So:

gorden biru = curtain blue → blue curtain
tikar kecil = mat small → small mat

More examples:

rumah besar = big house
buku baru = new book
mobil merah = red car

Putting the adjective before the noun (like English blue curtain) is not normal Indonesian grammar.

Does ada gorden biru dan tikar kecil mean one curtain and one mat, or can it be plural?

By default, Indonesian does not mark singular vs plural.

ada gorden biru dan tikar kecil can mean:

there is a blue curtain and a small mat, or
there are blue curtains and small mats

To make plural more explicit, Indonesian often:

repeats the noun (reduplication):
- gorden-gorden = curtains
- tikar-tikar = mats
or uses numbers / quantifiers:
- beberapa gorden biru = several blue curtains
- dua tikar kecil = two small mats

Why is di lantai at the end? Could I say it earlier?

Word order in Indonesian is quite flexible with location phrases.

The sentence:

Di kamar kosku, ada gorden biru dan tikar kecil di lantai.

The main structure is:

[Place 1] + ada + [things] + [Place 2]

You can change it a bit:

Di kamar kosku, di lantai ada tikar kecil.
Di kamar kosku ada tikar kecil di lantai. (comma often dropped in speech)

But the original is very natural:

first: where in general (in my room)
then: what is there (a blue curtain and a small mat)
finally: extra detail where the mat is (on the floor)

Note: di lantai most naturally describes tikar kecil, not gorden biru.

Why is there a comma after Di kamar kosku? Is it required?

The comma after Di kamar kosku is mostly stylistic, not strictly required.

It separates:

the location phrase: Di kamar kosku = In my boarding room
from
the main clause: ada gorden biru dan tikar kecil di lantai = there is a blue curtain and a small mat on the floor.

In everyday writing and speech, many people would omit it:

Di kamar kosku ada gorden biru dan tikar kecil di lantai.

Both are acceptable. The meaning does not change.

Why don’t we repeat ada before tikar kecil? Could we say ada gorden biru dan ada tikar kecil?

You can say:

Di kamar kosku, ada gorden biru dan ada tikar kecil di lantai.

It is grammatically correct, but sounds a bit heavier and more emphatic.

Normally, Indonesian mentions ada once, then lists the things:

Ada gorden biru dan tikar kecil.
= There is a blue curtain and a small mat.

So the original sentence is more natural and fluent.

What is gorden? Is it a loanword, and are there other words for curtain?

gorden means curtain (especially cloth window curtains).
It is a loanword (ultimately from Dutch gordijn).

Other words:

tirai – also means curtain or blind; can sound a bit more general or formal.
In everyday speech, gorden is extremely common for home window curtains.

So:

gorden biru = blue curtain
tirai biru = also blue curtain, but gorden feels more colloquial in many contexts.

What does tikar mean, and what kind of object is it?

tikar is a mat, usually something you put on the floor to sit on.

Typical features:

made of woven materials (bamboo, pandan leaves, plastic, etc.)
spread on the floor for sitting, eating together, praying, etc.

So tikar kecil = a small mat.
It is not a thick carpet like many English rugs; more like a thin floor mat.

What is the difference between di, ke, and pada for locations?

These three are all prepositions, but they have different uses:

di = at / in / on (location, static)
- di kamar = in the room
- di lantai = on the floor
ke = to (movement toward a place)
- pergi ke kamar = go to the room
- duduk ke lantai (less common; usually duduk di lantai)
pada = at / on / in, but:
- more formal, often used with time or abstract things
- pada hari Senin = on Monday
- pada saya can mean to me / on me in some contexts

In your sentence, it must be di kamar kosku and di lantai, because you’re describing where things are, not where they are going.