Я доварила рис, пока мама накрывала на стол.

Доварила comes from доварить, which means to finish cooking or to cook something until it is done.

The prefix до- often adds the idea of bringing something to completion. So:

• варила рис = was cooking rice / cooked rice
• доварила рис = finished cooking the rice

In this sentence, the speaker is not just describing the process. She is saying that she completed the rice-cooking.

That is the past tense feminine singular ending.

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

• я доварил = I finished cooking it (said by a man)
• я доварила = I finished cooking it (said by a woman)
• мы доварили = we finished cooking it

So я доварила tells you that the speaker is female.

The same thing happens in мама накрывала: мама is feminine, so the verb is feminine too.

This is a very common Russian aspect question.

Here, накрывала is imperfective because it describes an action that was in progress at the same time as the other action.

So the idea is:

• I finished cooking the rice
• while Mom was setting the table

Russian often uses:

• perfective for the completed main event: доварила
• imperfective for the background or simultaneous ongoing action: накрывала

If you said пока мама накрыла на стол, it would sound odd in this context, because накрыла is perfective and sounds like a completed single event, not an ongoing background action.

Here пока means while.

So:

• Я доварила рис, пока мама накрывала на стол. = I finished cooking the rice while Mom was setting the table.

A useful warning: пока can also mean until in other sentences. Its meaning depends on the context and the aspect of the verbs.

In this sentence, because both actions are happening in the same general time frame and мама накрывала is imperfective, the natural meaning is while.

Накрывать на стол is a set expression meaning to lay the table / set the table / put food and dishes out.

Literally, на стол means onto the table, but you should learn накрывать на стол as a whole phrase.

It usually refers to preparing the table for a meal: putting out plates, food, cutlery, and so on.

A related form is:

• накрывать стол — also used for setting the table

The version with на стол strongly suggests putting things out for eating.

Because на стол uses the accusative case, which often shows movement toward a destination.

Compare:

• на стол = onto the table
• на столе = on the table

In накрывать на стол, the idea is that dishes and food are being placed onto the table, so на стол is the expected form.

It actually is in the accusative, because it is the direct object of доварила.

But рис is a masculine inanimate noun, and for nouns like that, the accusative singular looks exactly like the nominative singular.

So:

• nominative: рис
• accusative: рис

That is why there is no visible change.

Yes. Russian word order is flexible.

For example, you could also say:

• Пока мама накрывала на стол, я доварила рис.

This means the same thing.

The difference is mostly in focus and rhythm:

• Я доварила рис, пока мама накрывала на стол.
  starts with what I did
• Пока мама накрывала на стол, я доварила рис.
  starts with the time/background setting

Both are natural.

Yes, Russian often omits subject pronouns when they are clear from the verb form or the context.

So you could say:

• Доварила рис, пока мама накрывала на стол.

This is possible if it is already clear who is speaking.

However, я is often kept for clarity, emphasis, or simply because the speaker chooses to include it.

The infinitives are:

• доварить → доварила
• накрывать → накрывала

Notice the aspect pair idea:

• доварить = perfective
• доваривать = imperfective

and:

• накрыть = perfective
• накрывать = imperfective

This sentence uses:

• perfective доварила for the completed result
• imperfective накрывала for the simultaneous ongoing action

Yes, but it changes the meaning.

• Я варила рис, пока мама накрывала на стол
  = I was cooking rice while Mom was setting the table
• Я доварила рис, пока мама накрывала на стол
  = I finished cooking the rice while Mom was setting the table

So варила focuses on the process, while доварила emphasizes completion.

That aspect difference is very important in Russian.

Not necessarily exactly every second, but they overlapped in time.

The natural idea is:

• Mom was in the middle of setting the table
• during that time, I finished cooking the rice

So Russian is showing simultaneous background timing, not a precise second-by-second match.

Yes — it is a very good example of how Russian uses aspect in past narration.

The pattern is:

• perfective past for a completed event: доварила
• imperfective past for the ongoing background action: накрывала

This is one of the most useful patterns in Russian storytelling and everyday description. If you get comfortable with this contrast, a lot of Russian sentences become much easier to understand.