Sesampainya di kelas, saya menaruh flashdisk di samping monitor agar tidak lupa saat presentasi.

Sesampainya means something like upon arriving or when I arrived.

It comes from the root sampai (to arrive) with the pattern se-...-nya, which often gives a sense like as soon as or upon doing something.

So:

• Sesampainya di kelas = Upon arriving in the classroom
• very natural English translation: When I got to class

A very close alternative in Indonesian would be:

• Setelah sampai di kelas
• Saat sampai di kelas

But sesampainya di kelas sounds a bit smoother and more compact.

Because di and ke do different jobs:

• di = in / at
• ke = to / toward

In Sesampainya di kelas, the speaker has already arrived, so the location is now at/in the classroom, not to the classroom.

Compare:

• Saya pergi ke kelas = I go to class / to the classroom
• Saya ada di kelas = I am in the classroom

So after arriving, di kelas is the natural choice.

Taruh is the root word. Menaruh is the active verb form with the meN- prefix, which is very common in standard Indonesian.

So:

• taruh = root/base form
• menaruh = to put / to place

In a full standard sentence, Indonesian often uses the prefixed form:

• Saya menaruh flashdisk... = I put the flash drive...

In casual speech, people may sometimes say:

• Saya taruh flashdisk...

That is common conversational Indonesian, but menaruh is more standard in writing and careful speech.

Yes. Menaruh and meletakkan can both mean to put / to place.

• menaruh = common and natural
• meletakkan = a bit more formal or explicit, often closer to to place

So this sentence could also be:

• Sesampainya di kelas, saya meletakkan flashdisk di samping monitor...

That sounds fine too.
In everyday speech, menaruh often feels slightly more natural and less formal.

Yes. In everyday Indonesian, flashdisk is very commonly used for a USB flash drive.

Even though English speakers might say:

• USB drive
• thumb drive
• flash drive

Indonesian speakers very often say:

• flashdisk

So the sentence sounds natural.

Di samping monitor means beside the monitor or next to the monitor.

Breakdown:

• di = at/in
• samping = side
• monitor = monitor/screen

So literally it is at the side of the monitor.

Some related expressions:

• di samping = beside / next to
• di sebelah = beside / next to
• di depan = in front of
• di belakang = behind
• di atas = on top of
• di bawah = under

Agar means so that or in order that.

In this sentence:

• agar tidak lupa saat presentasi = so that I won’t forget during the presentation

It introduces a purpose:

• The speaker puts the flash drive next to the monitor
• for the purpose of not forgetting it later

Common alternatives:

• supaya = so that
• biar = so that / so

In many situations, agar and supaya are interchangeable.
Agar can sound a bit more formal or written than biar.

The subject is still understood to be saya.

Indonesian often omits repeated subjects when they are already clear from context. So:

• saya menaruh flashdisk ... agar tidak lupa ...

is understood as:

• I put the flash drive ... so that I won’t forget ...

A more explicit version could be:

• ... agar saya tidak lupa saat presentasi

But repeating saya is not necessary here.

Grammatically, the sentence does not state it explicitly, but it is understood from context: the speaker does not want to forget the flash drive or possibly to use/bring it for the presentation.

That kind of omission is normal in Indonesian when the meaning is obvious.

If you wanted to make it more explicit, you could say:

• ... agar tidak lupa membawa flashdisk itu saat presentasi
• ... agar tidak lupa menggunakannya saat presentasi

But the original sentence is perfectly natural because listeners can easily infer the missing idea.

Here saat presentasi means during the presentation or at presentation time.

• saat = when / during
• presentasi = presentation

So it refers to the time of the presentation.

Depending on context, English translations could be:

• during the presentation
• when presenting
• at presentation time

If you wanted to be more explicit in Indonesian, you could say:

• saat presentasi berlangsung = while the presentation is taking place
• saat saya presentasi = when I present / when I’m giving the presentation

But the shorter saat presentasi is very natural.

Yes, it is very normal.

Indonesian often puts a time expression or background clause at the beginning of the sentence, followed by the main action.

So the structure is:

• Sesampainya di kelas = time/background
• saya menaruh flashdisk di samping monitor = main action
• agar tidak lupa saat presentasi = purpose

This is similar to English:

• When I got to class, I put the flash drive next to the monitor so I wouldn’t forget it during the presentation.

You could change the order, but the original version sounds very natural and organized.

Yes. Some common alternatives are:

• Setelah sampai di kelas = after arriving in class
• Saat sampai di kelas = when arriving in class
• Begitu sampai di kelas = as soon as I arrived in class

All of these are understandable.
Sesampainya di kelas is a neat, slightly more polished way to say it.

It can mean either, depending on context.

• kelas can mean classroom
• kelas can also mean class in the sense of a lesson/course session

In this sentence, because the speaker puts something di samping monitor, it sounds like a physical place, so classroom is a very natural interpretation.

So:

• di kelas here is best understood as in the classroom or in class

It sounds fairly neutral standard Indonesian.

Why:

• sesampainya is a normal, slightly polished written/spoken form
• saya is neutral and polite
• menaruh is standard
• agar is a standard connector

So it would sound fine in writing, in conversation, or in a semi-formal context.

A more casual version might be something like:

• Pas sampai di kelas, saya taruh flashdisk di samping monitor biar nggak lupa waktu presentasi.

That is more colloquial because of:

• pas instead of sesampainya
• taruh instead of menaruh
• biar instead of agar
• nggak instead of tidak
• waktu instead of saat

Indonesian does not use articles like a, an, and the the way English does.

So:

• flashdisk can mean a flash drive or the flash drive
• monitor can mean a monitor or the monitor

The exact meaning depends on context.

In this sentence, English would usually add the articles naturally:

• I put the flash drive next to the monitor...

But Indonesian does not need them.

In theory, tidak lupa by itself does not name the subject, so context matters. But in this sentence, the most natural reading is definitely so that I don’t forget, because the main subject just before it is saya.

So learners should understand the implied subject here as the speaker:

• saya menaruh ... agar [saya] tidak lupa ...

That kind of subject carryover is very common in Indonesian.