Learn Hardcore Indonesian: Di dinding kantor ada kertas kuning dan ungu. - On the office wall there are yellow and purple papers.

In Indonesian, di marks a location in general and is used for “in/at/on” depending on context. Di dinding means “on the wall” in the sense of being attached to the wall’s surface. Di atas dinding means “on top of the wall” (on the upper edge or the top surface), which is a different meaning.

What does ada do here?

Ada introduces existence: “there is/are.” So ada kertas… = “there is/are paper…”. It’s not the copula “to be.” Don’t use adalah here; adalah links two noun phrases (e.g., X adalah Y), not existence at a location.

Can I switch the word order to “Ada kertas kuning dan ungu di dinding kantor”?

Yes. Di dinding kantor ada… and Ada … di dinding kantor are both natural. Fronting the place (Di dinding kantor…) slightly emphasizes the location; starting with Ada… emphasizes the existence of the items.

Could I use berada or terdapat instead of ada?

Berada = “to be located,” more formal, and usually used with a definite/known subject: Kertas itu berada di dinding kantor.
Terdapat = formal “there is/are, can be found”: Terdapat kertas…
With an indefinite thing (“some paper”), ada is the default and most natural.

How do I show “a/the” in Indonesian when there are no articles?

Indonesian has no articles. Use other tools:

Indefinite one: selembar kertas (“a sheet of paper”), sebuah kantor (“an office”).
Definite: add itu (“that/the”): kertas itu, dinding kantor itu.
Possessives also make things definite: dinding kantor kami (“our office wall”).

Is kertas singular or plural here?

Unmarked kertas can be singular or plural. To be explicit:

One sheet: selembar kertas.
Several sheets: beberapa lembar kertas.
Plural by reduplication: kertas-kertas (often stylistic; counting with lembar is more common).

Do I need a classifier for “paper”?

When you count paper, yes. Use lembar (most common) or helai:

selembar kertas (one sheet)
dua lembar kertas (two sheets)

Does kertas kuning dan ungu mean one paper that’s yellow-and-purple, or yellow paper and purple paper?

By default it means there are yellow and purple papers (two colors available). It can be ambiguous. To disambiguate:

Two kinds: ada kertas kuning dan kertas ungu / ada kertas kuning dan ada kertas ungu.
One item with both colors: ada kertas yang berwarna kuning dan ungu, or better: ada kertas dua warna, kuning dan ungu / kertas bermotif kuning dan ungu.

Why do adjectives come after the noun (kertas kuning, not kuning kertas)?

In Indonesian, descriptive adjectives follow the noun: kertas kuning, baju baru. With multiple adjectives, you can stack them (kertas kuning besar) or make it clearer with yang: kertas kuning yang besar.

Is dinding kantor the same as dinding di kantor?

Dinding kantor = “the office wall” (a noun–noun compound, suggests a wall belonging to/part of the office).
Dinding di kantor = “a wall at the office” (just located there).
In your sentence, di dinding kantor is the natural way to say “on the office wall.”

What’s the difference between dinding and tembok?

Both mean “wall,” but:

Dinding is general and often used for interior walls/surfaces.
Tembok often refers to a structural, usually exterior or masonry wall.
For “on the office wall,” dinding is the default.

How do I make the location clearly definite, like “on the wall of that office”?

Add itu or a possessor:

Di dinding kantor itu… (“on that office’s wall”)
Di dinding kantor kami… (“on our office wall”)

Why is di written separately here? I’ve seen di- attached to words elsewhere.

Two different things:

di (separate) = preposition “at/in/on”: di dinding, di kantor.
di- (attached) = passive verb prefix: ditulis, dibaca.
So location uses spaced di
- place.

Can I say kertas berwarna kuning dan ungu?

Yes. Berwarna makes the color meaning explicit: ada kertas berwarna kuning dan ungu (“there is paper colored yellow and purple”). It’s a bit more formal/explicit than just kertas kuning dan ungu.

How would I say “There are two sheets of yellow paper and three of purple on the office wall”?

Di dinding kantor ada dua lembar kertas kuning dan tiga lembar kertas ungu.