Learn Hardcore Malay: Di rumah, saya letak pensel, pen, dan pemadam dalam satu bekas. - At home, I put a pencil, a pen, and an eraser in one container.

di rumah can mean at home or in/at the house, depending on context.
If you want to stress inside the house (as opposed to outside), you might say dalam rumah or di dalam rumah.

So di rumah is a neutral way to say you are located at home / at the house.

Can di rumah go at the end of the sentence, like Saya letak pensel, pen, dan pemadam dalam satu bekas di rumah? Is there any difference?

Yes, that word order is also correct:

Di rumah, saya letak …
Saya letak … di rumah.

They both mean essentially the same thing. The difference is in focus:

Starting with Di rumah slightly emphasizes the place (at home).
Putting di rumah at the end feels more neutral and is probably more common in everyday speech.

Grammatically, both are fine.

Why is the verb letak used here and not meletakkan? Are they interchangeable?

Letak is the base verb meaning to put / to place.

In everyday spoken Malay, people very often use the bare verb:
Saya letak pensel… = I put the pencils…
In more formal or written Malay, you will more often see meletakkan with an object:
Saya meletakkan pensel dalam satu bekas.

So:

letak – common, especially in speech and informal writing.
meletakkan – more formal / careful Standard Malay.

In this sentence, they are effectively interchangeable in meaning; the difference is mainly style and formality.

How is tense shown here? Does saya letak mean I put, I am putting, or I will put?

On its own, saya letak is not marked for tense. It can mean:

I put (habitually or generally)
I am putting (right now)
I will put (future)

Malay usually shows time by adding time words or particles, for example:

Semalam di rumah, saya letak… = Yesterday at home, I put…
Sekarang di rumah, saya sedang letak… = Right now at home, I am putting…
Esok di rumah, saya akan letak… = Tomorrow at home, I will put…

Without those clues, the time reference is understood from context.

Why are there no plural endings on pensel, pen, and pemadam? How do you show plural in Malay?

Malay normally does not change the noun form for plural. So:

pensel can mean a pencil or pencils
pen can mean a pen or pens
pemadam can mean an eraser or erasers

To show plural more clearly, Malay uses other strategies, for example:

Reduplication: pensel-pensel (pencils), pemadam-pemadam (erasers)
Quantifiers: beberapa pensel (several pencils), banyak pen (many pens), semua pemadam (all the erasers)
Numbers + classifiers: tiga batang pensel (three pencils), dua batang pen (two pens)

In your sentence, the list naturally suggests more than one of each, even though the nouns look singular.

What exactly does pemadam mean? Does it always mean an eraser?

Pemadam comes from padam (to erase / to extinguish) with a prefix that turns it into something that erases / extinguishes.

Its meaning depends on context:

In a school / stationery context, pemadam usually means (pencil) eraser.
- pemadam pensel = pencil eraser / rubber
In a fire-safety context, pemadam often appears in:
- pemadam api = fire extinguisher

In your sentence (together with pensel and pen), it clearly means eraser.

What is the difference between pensel and pen in Malay? Are there more specific words?

pensel = pencil (graphite writing instrument)
pen = pen (ink writing instrument), borrowed directly from English

More specific or related terms include:

pensel kayu = wooden pencil
pensel mekanik / pensel tekan = mechanical pencil
pen mata bola = ballpoint pen
pen mata dakwat kekal / pen marker = permanent marker (depending on variety)
pena = a more formal / literary word for pen; in everyday speech pen is more common.

In the sentence as given, pensel and pen are just the everyday basic words.

In dalam satu bekas, what does satu do? Could I just say dalam bekas? And what about sebuah bekas?

Satu literally means one, but very often functions like a / one in English.

dalam satu bekas = in one container / in a container
dalam bekas = in the container or in a container (more context-dependent)

So:

Using satu:
- Emphasizes that it is one single container.
- Also often gives the sense of an indefinite thing, like a container.

Sebuah is a classifier:

sebuah bekas = one (piece of) container, often translated simply as a container.
It’s slightly more formal / careful than just satu bekas, but both are widely used.

All of these are possible:

dalam satu bekas
dalam sebuah bekas
dalam bekas

The choice affects nuance (one vs some container vs a specific known container), not basic grammar.

What is the difference between dalam, di dalam, and ke dalam?

They are related but not identical:

dalam
- Can mean in / inside / within.
- dalam satu bekas = in one container.
di dalam
- di (at/in) + dalam (inside) = emphasizes being inside something.
- Often used like inside (of):
  Saya letak pensel di dalam satu bekas.
  = I put the pencils inside a container.
ke dalam
- ke (to, towards) + dalam (inside) = into, focusing on movement toward the inside.
- Saya masukkan pensel ke dalam satu bekas.
  = I put the pencils into a container.

In your sentence, dalam satu bekas focuses on the final location. You could say di dalam satu bekas without really changing the meaning. Ke dalam is more about the motion going inside.

Is the comma before dan in pensel, pen, dan pemadam required in Malay?

In Malay, the usual rule is:

Use commas between items in a list.
Do not normally put a comma directly before dan when it joins the last two items.

So the most typical written form is:

pensel, pen dan pemadam

However:

Writing pensel, pen, dan pemadam is not grammatically wrong; it’s more of a stylistic choice.
Many style guides prefer to omit the comma before dan, like standard Malay practice.

For everyday use, you can safely write pensel, pen dan pemadam.

Could I drop saya and just say Di rumah, letak pensel, pen, dan pemadam dalam satu bekas?

In formal or standard Malay, you normally keep the subject:

Di rumah, saya letak pensel…

Dropping saya is more like casual spoken Malay, where the subject is sometimes omitted if it’s obvious from context. So:

Di rumah, letak pensel… can occur in informal speech, but sounds incomplete if you see it as a full written sentence.
In writing or when learning, it’s safer and more natural to keep saya:
Di rumah, saya letak pensel, pen dan pemadam dalam satu bekas.