Когда поезд останавливается, пассажиры выходят из вагона на платформу.

Когда means when.

In this sentence, it introduces a time clause:

• Когда поезд останавливается = When the train stops
• пассажиры выходят из вагона на платформу = the passengers go out of the carriage onto the platform

So когда works just like English when at the beginning of a clause.

Russian uses a comma to separate a subordinate clause from the main clause.

So:

• Когда поезд останавливается, = subordinate clause
• пассажиры выходят из вагона на платформу. = main clause

This is very normal in Russian. Even though English sometimes feels similar here, Russian punctuation is more consistent about using the comma in this type of sentence.

This is a very common Russian aspect question.

• останавливается = imperfective, present tense
• остановится = perfective, future meaning

In this sentence, останавливается is used because the sentence describes a general repeated situation or a usual sequence of events:

• When the train stops, passengers get out...

This is not about one single completed future stop, but about what normally happens.

If you said:

• Когда поезд остановится, пассажиры выйдут...

that would mean something more like:

• When the train has stopped / when the train stops (in the future), the passengers will get out.

So the original sentence sounds more general or habitual.

The verb останавливаться means to stop in the sense of come to a stop.

The -ся ending often makes a verb reflexive or intransitive. Here it helps give the idea that the train itself is stopping, rather than someone stopping something else.

Compare:

• останавливать = to stop something
• останавливаться = to stop, come to a stop

So:

• Машинист останавливает поезд = The driver stops the train
• Поезд останавливается = The train stops

Because поезд is the subject of the clause, so it is in the nominative case.

In:

• поезд останавливается

the train is the thing doing the action, so nominative is required.

The same is true for:

• пассажиры выходят

Here пассажиры is also nominative, because the passengers are the subject of that verb.

Because пассажиры is plural, so the verb must also be plural.

• пассажир = passenger
• пассажиры = passengers

And:

• выходит = he/she/it goes out
• выходят = they go out

So пассажиры выходят means the passengers go out / get out.

Because the preposition из requires the genitive case.

• dictionary form: вагон
• genitive singular: вагона

So:

• из вагона = out of the carriage / from the carriage

This is a very important pattern to remember:

• из + genitive = out of / from inside
• с + genitive = off / from a surface
• от + genitive = away from

Here the passengers are coming out from inside the train car, so из is the correct preposition.

• поезд = train
• вагон = train car / carriage

So the sentence first talks about the whole train:

• Когда поезд останавливается = When the train stops

Then it talks about where the passengers come from:

• из вагона = out of the carriage

This makes sense because passengers physically leave a carriage, not the entire train as one abstract unit.

Because this sentence describes movement toward a destination, not location.

Russian often uses:

• на + accusative = motion onto/to
• на + prepositional = location on/at

So:

• на платформу = onto the platform / to the platform
• на платформе = on the platform

In this sentence, the passengers are moving onto the platform, so Russian uses the accusative:

• платформа → платформу

Compare:

• Пассажиры выходят на платформу. = The passengers go out onto the platform.
• Пассажиры стоят на платформе. = The passengers are standing on the platform.

Because they express two different parts of the movement:

• из вагона = where the movement starts from
• на платформу = where the movement goes to

So together they give the full path:

• The passengers go out of the carriage onto the platform.

Russian often makes these movement relationships very explicit.

It can mean both, depending on context.

• выходить / выйти literally means to go out / come out
• In transport contexts, it is often naturally translated as get out or get off

So in this sentence, English might say:

• The passengers get out of the carriage onto the platform
• The passengers get off the train and onto the platform

But the Russian verb itself is still выходят.

Because Russian present tense is often used for habitual actions, general truths, or what usually happens.

This sentence describes a typical sequence:

• the train stops
• the passengers get out

So the present tense is completely natural.

Russian uses the present this way just like English does in sentences such as:

• When it rains, the streets get wet.
• When the train stops, passengers get out.

It does not necessarily mean this is happening right now.

Yes. Russian word order is fairly flexible, although the original order is very natural.

Original:

• Когда поезд останавливается, пассажиры выходят из вагона на платформу.

You could also say:

• Пассажиры выходят из вагона на платформу, когда поезд останавливается.

Both are grammatical. The difference is mostly about emphasis and style.

The version with Когда... first is a very natural way to present the time condition before the main action.

No. Russian has no articles.

So words like:

• поезд can mean the train or a train
• вагона can mean of the carriage or of a carriage
• платформу can mean the platform or a platform

You understand which one is meant from context. In this sentence, English naturally uses the:

• When the train stops, the passengers get out of the carriage onto the platform.

But Russian does not need a separate word for the.

Usually вагон means a rail car, train car, or carriage. In many contexts, yes, it refers to a part of a train.

Depending on context, it can also refer to other kinds of rail cars, and in some usage it can even have extended meanings, but for a learner, the safest understanding here is:

• вагон = train car / carriage

So из вагона is very naturally out of the carriage.

A helpful stressed version is:

Когда́ по́езд остана́вливается, пассажи́ры выхо́дят из ваго́на на платфо́рму.

Main stresses:

• когда́
• по́езд
• остана́вливается
• пассажи́ры
• выхо́дят
• ваго́на
• платфо́рму

This can help a lot with pronunciation and listening.