Пока мама готовит ужин, я накрою на стол.

Here пока means while.

So:

• Пока мама готовит ужин = While Mom is cooking dinner
• я накрою на стол = I’ll set the table

A useful thing to know is that пока can also mean for now or sometimes until, depending on context. But in this sentence, with two actions happening in the same general time frame, it means while.

In Russian, the present-tense form of an imperfective verb is often used after пока to mean something like while someone is doing something.

So мама готовит ужин literally looks like Mom cooks/is cooking dinner, but in this context it means:

• while Mom is cooking dinner

This is natural in Russian. English often uses a future-related form in the whole sentence, but Russian does not need to make both verbs future.

Накрою is the perfective future form of накрыть. It shows a single completed action:

• я накрою на стол = I’ll set the table

The speaker means they will do the task and finish it.

Compare:

• накрою = I’ll set the table / I’ll get the table ready
• буду накрывать = I’ll be setting the table / focus on the process

Russian often chooses the perfective future when the result matters.

Because the sentence presents the two actions differently:

• готовит is imperfective: it describes an ongoing process
  
  • Mom is in the middle of cooking dinner.
• накрою is perfective: it describes a completed action
  
  • I will set the table.

So the idea is:

• While Mom is busy cooking, I’ll get the table set.

This combination is very common in Russian: one ongoing background action plus one completed action.

This is an idiomatic expression meaning:

• I’ll set the table
• I’ll lay the table
• sometimes more literally, I’ll put the food/tableware out

The verb is from накрыть / накрывать на стол, a common Russian expression connected with preparing the table for a meal.

So even though the literal pieces may not match English perfectly, the whole phrase should be learned as a set expression.

Because накрывать / накрыть на стол is a fixed expression in Russian.

• на стол literally means onto the table
• but the whole phrase means to set the table / put things out for a meal

A learner might expect накрыть стол, and that can also exist in Russian, but накрыть на стол is a very common expression meaning to prepare or serve the table for eating.

So it is best to learn:

• накрывать на стол = to set the table
• накрыть на стол = to set the table / put everything out

Ужин is in the accusative case because it is the direct object of готовит.

• готовит что? → ужин
• She is cooking what? → dinner

For an inanimate masculine noun like ужин, the accusative looks the same as the nominative:

• nominative: ужин
• accusative: ужин

So the form does not change, but the case function is accusative.

Мама is in the nominative case because it is the subject of the clause.

• мама готовит ужин = Mom is cooking dinner

Even though мама ends in -а, it is a normal noun in the nominative singular here.

Because Пока мама готовит ужин is a subordinate clause, and Russian normally separates subordinate clauses with a comma.

So:

• Пока мама готовит ужин, я накрою на стол.

This is the standard punctuation.

English also often uses a comma when the while clause comes first:

• While Mom is cooking dinner, I’ll set the table.

Yes. Russian word order is flexible.

You could also say:

• Я накрою на стол, пока мама готовит ужин.

This means essentially the same thing.

The version with Пока... first sounds natural because it sets the time/background first, then gives the main action.

Yes, very often.

Russian often leaves out subject pronouns when they are clear from the verb ending. So:

• Пока мама готовит ужин, накрою на стол.

is also possible.

Including я can add clarity, contrast, or a slightly more explicit tone:

• Mom is cooking, and I’ll set the table.

So both are possible, but я is not always necessary.

Usually ужин is translated as dinner or supper, depending on the variety of English and the family’s eating habits.

In most learner translations, dinner is the safest choice:

• Пока мама готовит ужин, я накрою на стол.
• While Mom is cooking dinner, I’ll set the table.

Yes, in many contexts Russian uses мама without a possessive pronoun, where English often says Mom or my mom.

So мама готовит ужин naturally means:

• Mom is cooking dinner
• or My mom is cooking dinner

Russian does not need a word for my here if the relationship is obvious from context.

Yes, пока can sometimes mean until, but not in this sentence.

For example:

• Подожди, пока мама придёт.
• Wait until Mom comes.

But here the sentence clearly describes one action happening during another:

• While Mom is cooking dinner, I’ll set the table.

So here пока means while, not until.