Tren gelince önce ön vagona bindik, çünkü arka vagon çok doluydu.

Gelince comes from gelmek = to come / to arrive.

The ending -ince / -ınca / -unca / -ünce usually means when, once, or upon doing something.

• gelmek → gelince = when it comes/came, when it arrived
• bitmek → bitince = when it finishes/finished

So Tren gelince means when the train arrived.

A useful point: -ince itself does not translate into one fixed English tense. The tense is understood from the whole sentence.

Because binmek takes the dative case, not the direct object.

• vagona = to / onto the carriage
• vagonu would be the accusative, and that is not used with binmek

In Turkish, you board onto something:

• trene binmek = to get on the train
• otobüse binmek = to get on the bus
• arabaya binmek = to get in the car

So ön vagona bindik is the correct pattern.

They are related in meaning, but they do different jobs.

• önce = first, beforehand, before
• ön = front

So:

• önce tells you the order of the action: first
• ön vagon tells you which carriage: front carriage

That is why önce ön vagona bindik means something like we first got on the front carriage.

To an English speaker, the repetition may feel a little odd, but in Turkish it is perfectly normal.

Because the two noun phrases have different roles in the sentence.

1. ön vagona

This is the thing boarded, so it follows binmek and takes the dative ending:

• ön vagon = front carriage
• ön vagona = onto the front carriage

2. arka vagon

This is the subject of the second clause:

• arka vagon çok doluydu = the rear carriage was very full/crowded

Subjects normally appear with no extra case ending, so vagon stays unchanged.

Bindik breaks down like this:

• bin- = get on / board
• -di- = past tense
• -k = we

So bindik means we got on / we boarded.

That is also why Turkish does not need a separate biz here. The verb ending already tells you the subject is we.

• bindim = I got on
• bindin = you got on
• bindi = he/she/it got on
• bindik = we got on

You could add biz for emphasis, but it is not necessary.

Because these mean different things.

• dolu = full
• doluydu = was full
• doldu = became full, filled up

In this sentence, the speaker is describing the state of the rear carriage, not the moment it filled up. So çok doluydu means it was very full / crowded.

Grammatically, doluydu is:

• dolu
  • -ydu = past form of to be

So it literally works like was full.

Çünkü means because.

It introduces the reason:

• Önce ön vagona bindik = we first got on the front carriage
• çünkü arka vagon çok doluydu = because the rear carriage was very crowded

This is a very common and straightforward way to give a reason in Turkish.

Turkish also has another common pattern:

• Arka vagon çok dolu olduğu için önce ön vagona bindik.

That also means We first got on the front carriage because the rear carriage was very crowded.

Because Turkish does not have articles like a, an, and the.

So words like:

• tren
• vagon
• arka vagon

do not need a separate word for the.

Whether English uses a or the depends on context. In this sentence, the context makes it natural to translate them as the train, the front carriage, and the rear carriage.

It can mean both.

Literally, çok dolu means very full. But when talking about places, vehicles, rooms, or train cars, English often prefers very crowded or packed.

So for arka vagon çok doluydu, good English translations include:

• the rear carriage was very full
• the rear carriage was very crowded
• the rear carriage was packed

All are possible, depending on the style of translation.

Turkish word order is fairly flexible, but this sentence is in a very natural order.

It goes:

1. time: Tren gelince = when the train arrived
2. main action: önce ön vagona bindik = we first boarded the front carriage
3. reason: çünkü arka vagon çok doluydu = because the rear carriage was very crowded

This order is clear and natural.

You can express the same idea in other ways, for example:

• Arka vagon çok dolu olduğu için tren gelince önce ön vagona bindik.

But the original sentence is probably the easiest and most direct version for a learner.