Begitu kancing baju saya lepas, saya langsung mencari jarum dan benang di lemari.

Here begitu works like a conjunction meaning as soon as or once.

So:

• Begitu kancing baju saya lepas, ... = As soon as my shirt button came off, ...

In other contexts, begitu can also mean like that or that way, but in this sentence it introduces an event that is immediately followed by another one.

Not exactly.

• ketika / saat = when
• begitu = as soon as / once

So begitu gives a stronger sense of immediacy.

Compare:

• Ketika kancing baju saya lepas, saya mencari jarum dan benang. = When my shirt button came off, I looked for a needle and thread.
• Begitu kancing baju saya lepas, saya langsung mencari jarum dan benang. = As soon as my shirt button came off, I immediately looked for a needle and thread.

The second one sounds more immediate and connected.

Indonesian noun phrases usually go from the main noun to the thing that describes or possesses it.

So:

• kancing = button
• baju = shirt/clothes
• saya = my

Putting them together:

• kancing baju = shirt button / button of a shirt
• kancing baju saya = my shirt’s button / the button on my shirt

The head noun is kancing, and baju saya tells you which button.

This structure is very common in Indonesian:

• pintu rumah saya = my house door
• warna mobilnya = the color of his/her car
• nama teman saya = my friend’s name

Here lepas means come off, be detached, or become loose/off.

So kancing baju saya lepas means the button was no longer attached.

A useful point: lepas can behave like an adjective or an intransitive verb depending on context. In everyday Indonesian, that distinction is often less rigid than in English.

Examples:

• Tali sepatu saya lepas. = My shoelace came undone.
• Roda mobil itu lepas. = That car’s wheel came off.

So in this sentence, lepas describes the button’s state/change of state.

Because Indonesian usually does not need a copula like is/are/was/were in simple statements.

English says:

• My shirt button was loose
• My shirt button came off

Indonesian can simply say:

• Kancing baju saya lepas

This is normal. Indonesian often leaves out to be entirely when it is not necessary.

For example:

• Dia sakit. = He/She is sick.
• Rumah itu besar. = That house is big.
• Kancingnya lepas. = The button came off / is detached.

Time is usually understood from context, not from a verb tense ending.

Langsung means immediately, right away, or straightaway.

In this sentence it emphasizes that the speaker reacted without delay:

• saya langsung mencari ... = I immediately looked for ...

Without langsung, the sentence would still make sense, but it would lose some urgency.

Compare:

• Saya mencari jarum dan benang. = I looked for a needle and thread.
• Saya langsung mencari jarum dan benang. = I immediately looked for a needle and thread.

Mencari is the standard meN- verb form from cari.

• cari = the root
• mencari = to look for / to search for

In careful or neutral standard Indonesian, mencari is the expected form after saya:

• saya mencari = I look for / looked for / am looking for

In casual speech, people often drop the prefix and say:

• saya cari
• langsung cari

That is common in conversation, but mencari is more standard and is the better form for learners to recognize and produce first.

Indonesian nouns usually do not change form for singular vs. plural, and there are no articles like a/an/the in the same way English has them.

So:

• jarum can mean needle or needles
• benang can mean thread or threads

Context tells you what is meant. In this sentence, English naturally translates it as a needle and thread, but Indonesian does not need special words for that.

If you really want to mark plurality, Indonesian can do so in other ways, for example:

• jarum-jarum = needles
• beberapa jarum = several needles

But none of that is necessary here.

Di lemari tells you where the speaker looked for the needle and thread.

So the structure is:

• saya langsung mencari jarum dan benang
• di lemari

Together:

• I immediately looked for a needle and thread in the cupboard/closet.

It most naturally attaches to mencari, not to jarum dan benang as a description.

In other words, it means:

• I looked in the cupboard for a needle and thread,
  not
• I looked for the needle and thread that were in the cupboard
  unless context makes that interpretation clear.

Lemari is a general word for a storage cabinet, cupboard, wardrobe, or closet, depending on context.

Possible translations include:

• cupboard
• cabinet
• wardrobe
• closet

So di lemari could mean:

• in the cupboard
• in the cabinet
• in the wardrobe/closet

The best English choice depends on what kind of lemari the speaker means in the situation.

Yes. Indonesian allows some flexibility.

The original order:

• Begitu kancing baju saya lepas, saya langsung mencari jarum dan benang di lemari.

You could also say:

• Saya langsung mencari jarum dan benang di lemari begitu kancing baju saya lepas.

Both are understandable. The original version sounds very natural because it sets up the triggering event first, then gives the reaction.

That pattern is very common in Indonesian:

• Begitu dia datang, kami mulai makan.
• Begitu hujan turun, mereka masuk rumah.

Sometimes yes, but the nuance changes a little.

• lepas = loose, detached, off; came off
• terlepas = became detached / accidentally got detached / was detached

So:

• Kancing baju saya lepas sounds simple, natural, and everyday.
• Kancing baju saya terlepas sounds a bit more formal or more explicitly like it got detached.

In casual speech, lepas is very common and completely natural here.

It is mostly neutral standard Indonesian.

Why:

• begitu is normal and natural
• langsung is everyday but standard
• mencari uses the full standard verb form
• the structure is clear and grammatical

In more casual spoken Indonesian, someone might say:

• Begitu kancing baju saya lepas, saya langsung cari jarum sama benang di lemari.

That is more colloquial because:

• cari replaces mencari
• sama replaces dan

But the original sentence is a very good model of standard everyday Indonesian.