Pintu depan itu terkunci, jadi kami menunggu di luar.

In Indonesian, demonstratives like ini and itu usually come after the noun:

• pintu itu = that door / the door
• rumah ini = this house

So pintu depan itu literally looks like door front that, but naturally it means that front door or the front door.

In real usage, itu can sometimes feel like English that, but it can also simply help point to a specific known thing, almost like the.

Indonesian often leaves out the verb to be when describing something.

So:

• Pintu depan itu terkunci
  literally: The front door locked natural English: The front door is locked

This is very normal in Indonesian. You also see it in sentences like:

• Dia sakit = He/She is sick
• Rumahnya besar = His/Her house is big

You do not need a separate word for is here.

Terkunci means locked.

It comes from the root kunci, which means lock or key, depending on context.

In this sentence, terkunci describes the state of the door: it is in a locked condition.

So:

• Pintu itu terkunci = The door is locked

This is different from focusing on the action of someone locking it.

This is a very common learner question.

• terkunci usually describes a state/result: locked
• dikunci usually emphasizes the action done to it: locked by someone

Compare:

• Pintu itu terkunci = The door is locked
  focus: its condition
• Pintu itu dikunci oleh penjaga = The door was locked by the guard
  focus: the action and possibly the doer

In your sentence, the important idea is the condition of the door, so terkunci is the natural choice.

Depan means front.

So:

• pintu depan = front door
• literally: door front

Indonesian often puts the main noun first and the describing word after it.

Compare:

• mobil baru = new car
• rumah besar = big house
• pintu depan = front door

So the order is normal Indonesian word order.

Jadi here means so, therefore, or as a result.

It connects the first clause to the consequence:

• Pintu depan itu terkunci = the front door was/is locked
• jadi kami menunggu di luar = so we waited outside

So jadi introduces the result of the first situation.

It is not the same as karena:

• karena = because
• jadi = so

Compare:

• Kami menunggu di luar karena pintu depan itu terkunci.
  We waited outside because the front door was locked.
• Pintu depan itu terkunci, jadi kami menunggu di luar.
  The front door was locked, so we waited outside.

Indonesian has two different words for we:

• kami = we, but not including the listener
• kita = we, including the listener

So kami menunggu di luar means:

• we waited outside, but you were not part of our group

If the speaker wanted to include the person they were talking to, they would use kita instead.

This distinction is very important in Indonesian.

Menunggu means to wait or to be waiting.

Its root is tunggu = wait.

The prefix meN- forms an active verb, so:

• tunggu = wait
• menunggu = to wait / waiting

In this sentence:

• kami menunggu di luar = we waited outside

The object does not have to be stated. Indonesian often leaves out things that are obvious from context. Here, English might say waited outside, and Indonesian does the same.

Because di here is a preposition meaning in/at/on, not a verb prefix.

• di luar = outside
• di rumah = at home
• di jalan = on the street

When di is a preposition showing location, it is written separately.

Compare that with the prefix di- used in passive verbs, which is written together:

• dikunci = locked / was locked
• dibuka = opened
• ditulis = written

So:

• di luar = correct
• diluar = nonstandard in formal writing

Yes. Literally it is:

• di = at/in
• luar = outside, exterior

So di luar means outside or outdoors, depending on context.

In this sentence:

• kami menunggu di luar = we waited outside

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

So the sentence itself does not explicitly mark past or present. Depending on context, it could be understood as:

• The front door is locked, so we are waiting outside
• The front door was locked, so we waited outside

Usually the surrounding context tells you which time is meant. Since your English meaning is already given, the Indonesian sentence simply leaves tense unmarked.

Yes, often it can.

• Pintu depan terkunci = The front door is locked
• Pintu depan itu terkunci = That/the front door is locked

Adding itu makes the noun more specific or more clearly identifiable. Without it, the sentence is still natural, but slightly less pointed.

So both are possible, depending on context.

Yes. One very natural alternative is:

• Kami menunggu di luar karena pintu depan itu terkunci.

This means:

• We waited outside because the front door was locked.

The difference is just in how the information is organized:

• ..., jadi ... = ..., so ...
• ... karena ... = ... because ...

Both are common and natural.