Пока я ждал врача, я листал журнал в коридоре.

Because пока я ждал врача is a subordinate clause introduced by пока. In Russian, a subordinate clause is normally separated from the main clause with a comma.

So the sentence is divided like this:

• Пока я ждал врача = while I was waiting for the doctor
• я листал журнал в коридоре = I was flipping through a magazine in the corridor

Even if the subordinate clause comes first, the comma is still needed.

Here пока means while.

So:

• Пока я ждал врача = While I was waiting for the doctor

Be careful, because пока can also mean other things in different contexts, such as:

• for now / for the time being
• bye in informal speech
• sometimes until, depending on structure

But in this sentence, it clearly means while, introducing an action happening at the same time as another action.

Ждал is the past tense masculine singular form of ждать.

Russian past tense agrees with gender and number:

• я ждал = I waited / I was waiting (male speaker)
• я ждала = I waited / I was waiting (female speaker)
• мы ждали = we waited / were waiting

So this sentence suggests that the speaker is male. If the speaker were female, it would be:

• Пока я ждала врача, я листала журнал в коридоре.

Because врач is the object of ждал (waited for), so it is in the accusative case.

For masculine animate nouns, the accusative singular often looks like the genitive singular:

• nominative: врач
• accusative: врача

Since a doctor is an animate person, Russian uses врача here.

Compare:

• Я ждал врача. = I was waiting for the doctor.
• Я видел врача. = I saw the doctor.

But with an inanimate masculine noun, accusative often looks like nominative:

• Я читал журнал.

Because the sentence describes two ongoing, simultaneous past actions.

• ждал = was waiting
• листал = was flipping through

The imperfective aspect is natural here because the focus is on the process, not on completion.

This is very common with while-type sentences:

• Пока я ждал..., я листал...

If you used perfective forms, the meaning would change and would sound less natural for this situation, because perfective usually points to a completed event.

Листал comes from листать, which means something like:

• to flip through
• to leaf through

It suggests the person was turning pages casually, not necessarily reading carefully from start to finish.

Читал simply means was reading.

So:

• я листал журнал = I was flipping through a magazine
• я читал журнал = I was reading a magazine

In a waiting-room situation, листал журнал sounds very natural, because people often just browse a magazine rather than read it closely.

They are in different cases because they have different roles in the sentence.

• журнал is the direct object of листал, so it is in the accusative
• в коридоре shows location, so it uses в + prepositional

Breakdown:

• листал что? → журнал
• где? → в коридоре

The noun коридор changes like this:

• nominative: коридор
• prepositional: в коридоре

So в коридоре means in the corridor.

In practice, it most naturally describes the setting of the main situation, and it can easily be understood as applying to the whole scene.

So the idea is:

• while I was waiting for the doctor,
• I was in the corridor,
• and there I was flipping through a magazine

Russian often allows this kind of natural attachment without spelling everything out separately.

If you wanted to make the location more explicitly tied to the whole situation, you could still keep the same sentence; the original already sounds natural.

Yes. Russian word order is flexible.

The original sentence is neutral and natural:

• Пока я ждал врача, я листал журнал в коридоре.

But you could also say:

• Я листал журнал в коридоре, пока ждал врача.
• В коридоре я листал журнал, пока ждал врача.

These variations change emphasis slightly:

• putting в коридоре earlier highlights the location
• putting the пока clause later makes the main action come first

Russian uses word order not only for grammar, but also for focus and style.

Sometimes yes, especially in informal speech, because the subject is already clear from context.

For example:

• Пока я ждал врача, листал журнал в коридоре.

A Russian speaker may say this, and it can sound natural in conversation if it is obvious that the same person is doing both actions.

However, the full version with both я is clearer and very normal:

• Пока я ждал врача, я листал журнал в коридоре.

For learners, keeping the pronoun is usually safer.

In English, the best match is usually I was waiting, because Russian imperfective past often corresponds to an ongoing past action.

So:

• Пока я ждал врача... = While I was waiting for the doctor...
• я листал журнал... = I was flipping through a magazine...

Russian does not have a separate tense exactly like the English past continuous, so the imperfective past often covers that meaning.

Yes. Russian has no articles, so врача can mean either a doctor or the doctor, depending on context.

In this sentence, English often uses the doctor because the situation is probably specific: you are waiting for an appointment. But Russian itself does not mark that distinction with an article.

So the context tells you whether to understand it as:

• a doctor
• the doctor

Both are grammatically possible in Russian.