Begitu pintu dibuka, kami masuk ke ruang tamu.

In this sentence, begitu means as soon as or once.

So Begitu pintu dibuka means As soon as the door was opened / opened.

A useful pattern is:

• Begitu + clause, ... = As soon as + clause, ...

Examples:

• Begitu saya sampai, saya menelepon. = As soon as I arrived, I called.
• Begitu hujan turun, kami masuk. = As soon as it started raining, we went inside.

Dibuka is the passive form of membuka.

• membuka = to open
• dibuka = be opened / opened

In Begitu pintu dibuka, the focus is on the door being opened, not on who opened it.

Compare:

• Begitu pintu dibuka, kami masuk...
  = As soon as the door was opened, we went in...

• Begitu dia membuka pintu, kami masuk...
  = As soon as he/she opened the door, we went in...

So Indonesian often uses the passive when the doer is unknown, unimportant, or obvious from context.

Yes, the sentence does not say who opened the door.

That is normal in Indonesian. With a di- passive form like dibuka, the agent can be left unstated.

If you want to include the agent, you could say:

• Begitu pintu dibuka oleh penjaga, kami masuk ke ruang tamu.
  = As soon as the door was opened by the guard, we entered the living room.

But very often Indonesian leaves that out if it is not important.

They are similar, but not exactly the same.

• begitu pintu dibuka = as soon as the door was opened
• setelah pintu dibuka = after the door was opened

Begitu gives a stronger sense of immediate sequence. It suggests that the second action happened right away.

So:

• Begitu pintu dibuka, kami masuk...
  = The moment the door opened, we went in.

• Setelah pintu dibuka, kami masuk...
  = After the door was opened, we went in.
  This does not stress immediacy as much.

You can, but the meaning changes a little.

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

Compare:

• Ketika pintu dibuka, kami masuk ke ruang tamu.
  = When the door was opened, we entered the living room.

• Begitu pintu dibuka, kami masuk ke ruang tamu.
  = As soon as the door was opened, we entered the living room.

Begitu sounds more immediate and more tightly connected in time.

Ke marks movement toward a place.

• masuk ke ruang tamu = enter/go into the living room

This is different from di, which marks location:

• di ruang tamu = in the living room

So:

• Kami masuk ke ruang tamu. = We went into the living room.
• Kami duduk di ruang tamu. = We sat in the living room.

In everyday speech, people may sometimes drop ke after masuk, but masuk ke ruang tamu is very clear and standard.

No, they are different.

• ruang tamu = living room / sitting room / reception room
• kamar tamu = guest bedroom

So in this sentence, ruang tamu refers to the room where guests are received, not a bedroom.

Also:

• ruang = room/space
• tamu = guest

Literally, ruang tamu is the guest room, but in actual usage it usually means living room or front room for receiving guests.

This is an important distinction in Indonesian:

• kami = we, excluding the listener
• kita = we, including the listener

So kami masuk ke ruang tamu means we entered the living room, but you were not part of that group.

If the listener was included, it would be:

• Begitu pintu dibuka, kita masuk ke ruang tamu.

English just says we, but Indonesian makes this difference explicit.

Indonesian verbs do not change form for tense the way English verbs do.

So dibuka and masuk do not themselves mean past, present, or future. The time is understood from:

• context
• time words
• the situation being described

In many contexts, this sentence will naturally be understood as past:

• Begitu pintu dibuka, kami masuk ke ruang tamu.
  = As soon as the door was opened, we entered the living room.

But in another context, it could also describe a habitual or future situation, depending on surrounding information.

Yes, Indonesian allows some flexibility.

The original order is very natural:

• Begitu pintu dibuka, kami masuk ke ruang tamu.

You could also say:

• Kami masuk ke ruang tamu begitu pintu dibuka.

This still means basically the same thing: We entered the living room as soon as the door was opened.

The original version puts the time clause first, which gives it a nice narrative flow: first the door opens, then we enter.

The comma separates the introductory clause from the main clause:

• Begitu pintu dibuka, = subordinate clause
• kami masuk ke ruang tamu. = main clause

This is similar to English:

• As soon as the door was opened, we entered the living room.

In informal writing, punctuation may be less strict, but the comma is standard and helpful here.

Yes. By itself, dibuka does not mark tense, so it can mean different things depending on context.

Possible interpretations include:

• is opened
• was opened
• gets opened
• has been opened

In this sentence, because it is part of a sequence of actions, English usually translates it as past:

• As soon as the door was opened, we entered the living room.

So the form stays the same in Indonesian, while English chooses the tense based on context.