Едва поезд остановился, как я вышел на платформу.

Here едва means something like hardly, scarcely, or barely had ... when ....

So the sentence has the sense:

Hardly had the train stopped when I stepped out onto the platform.

In modern English, that often gets translated more naturally as As soon as the train stopped, I got out onto the platform.

In this sentence, как is part of the correlative pattern едва ..., как ....

This structure links two events:

• Едва поезд остановился = Hardly had the train stopped
• как я вышел на платформу = when I stepped out onto the platform

So как here does not mean a simple how. It functions more like when in the English pattern hardly ... when ....

Yes, it is a very common pattern.

It expresses that the second action happened almost immediately after the first one. You can think of it as a set structure:

• Едва X, как Y
• Едва только X, как Y
• sometimes simply Едва X, Y

So this sentence follows a standard Russian way of saying no sooner ... than ... or hardly ... when ....

Because both actions happened in the past:

• остановился = stopped
• вышел = went out / stepped out

Russian does not need a special tense like the English had stopped here. The relationship between the actions is shown mainly by the structure едва ..., как ..., not by a separate past perfect tense.

So even though English often says Hardly had the train stopped, Russian simply uses the ordinary past tense.

Both verbs describe completed single events:

• остановился = the train came to a stop
• вышел = I went out / stepped out

Perfective aspect is natural here because the sentence focuses on the sequence of completed actions.

If you used imperfective forms, the meaning would change and sound less natural in this context, because you would no longer be talking about two clear, completed events that happened one right after the other.

Остановился is the intransitive/reflexive form meaning stopped.

• Поезд остановился = The train stopped
• Я остановил поезд = I stopped the train

So the -ся form is needed because the train itself came to a stop; no outside agent is mentioned.

Because на can take different cases depending on meaning:

• на платформу
  • accusative = motion onto / to the platform
• на платформе
  • prepositional = location on the platform

Here the speaker is moving outward onto the platform, so Russian uses the accusative:

• вышел на платформу = went out onto the platform

If you said я был на платформе, that would mean I was on the platform.

You can say just вышел if the destination is obvious from context, but на платформу makes it explicit: the speaker stepped out onto the platform.

This is very natural with verbs of movement in Russian. Russian often states the destination clearly:

• вышел на улицу = went out onto the street
• вышел на балкон = went out onto the balcony
• вышел на платформу = went out onto the platform

In the past tense, Russian verbs agree with the subject in gender and number.

• я вышел = I went out said by a man
• я вышла = I went out said by a woman

So the sentence as written implies a male speaker. If the speaker were female, it would be:

Едва поезд остановился, как я вышла на платформу.

Because this is a complex sentence with two clauses:

• Едва поезд остановился
• как я вышел на платформу

Russian normally separates such clauses with a comma. With the pattern едва ..., как ..., the comma is standard.

Yes, Russian word order is flexible, but the given version is the most neutral and natural.

The sentence starts with the time-linking clause:

• Едва поезд остановился, как я вышел на платформу.

This order emphasizes the immediate sequence: first the train stopped, then immediately I got out.

You may sometimes see slightly different arrangements in literary or expressive style, but for a learner, the original order is the safest model.

Not always. Едва can also mean barely in other contexts.

For example:

• Я едва успел на поезд. = I barely caught the train.

So едва has a broader meaning connected with something happening only just, with little margin.

In the structure едва ..., как ..., though, it specifically means something like hardly had ... when ....

Yes. That is a very good formal English translation.

Possible English versions include:

• Hardly had the train stopped when I stepped out onto the platform.
• No sooner had the train stopped than I got out onto the platform.
• As soon as the train stopped, I stepped out onto the platform.

They all match the Russian, though the first two preserve the stylistic feel of едва ..., как ... more closely.

Russian has no articles like a or the.

So:

• поезд can mean a train or the train
• платформа can mean a platform or the platform

Context tells you which one is meant. In this sentence, English naturally uses the train and the platform, because both are specific in the situation.