Перед ужином мама принесла поднос с тарелками и попросила меня накрыть на стол.

Because the preposition перед normally takes the instrumental case.

In time expressions, перед + instrumental means before:

• перед сном — before sleep / before bed
• перед уроком — before class
• перед ужином — before dinner

So:

• ужин = dinner
• ужином = instrumental singular of ужин

A literal sense is something like before dinner.

The past tense in Russian agrees with the subject in gender and number.

The subject here is мама, which is feminine singular, so the verb must also be feminine singular in the past:

• принёс — masculine
• принесла — feminine
• принесло — neuter
• принесли — plural

So мама принесла means mom brought.

Принести is the perfective verb, and here it fits because the sentence describes a completed action: she brought the tray.

Russian often uses perfective verbs for single finished events in a sequence:

• she brought the tray
• and asked me to set the table

That is why принесла sounds natural here.

The imperfective partner is приносила / приносить, which would suggest something like repeated action, process, or background description, depending on context.

Here с means with, and in that meaning it usually takes the instrumental case.

So:

• тарелки = plates
• с тарелками = with plates

Therefore:

• поднос с тарелками = a tray with plates

This is a very common pattern:

• чай с лимоном — tea with lemon
• девушка с сумкой — a girl with a bag
• коробка с игрушками — a box with toys

Поднос is the direct object of принесла, so it is in the accusative case.

However, for many inanimate masculine nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: поднос
• accusative: поднос

That is why the form does not visibly change.

After попросить in the sense of ask someone to do something, Russian commonly uses:

попросить + accusative person + infinitive

So:

• попросила меня накрыть на стол = she asked me to set the table

Here меня is accusative because I am the person being asked.

Compare:

• Она попросила меня помочь. — She asked me to help.
• Он попросил сестру позвонить. — He asked his sister to call.

A learner may expect мне because English has asked me, but Russian uses the accusative in this structure.

Yes. Russian can also use a clause with чтобы:

• мама попросила, чтобы я накрыл на стол

This also means mom asked me to set the table.

But the structure in your sentence:

• попросила меня накрыть на стол

is shorter and very common when the person asked is clear and the action is expressed with an infinitive.

Both patterns are natural.

This is an idiomatic Russian expression.

накрыть на стол means to set the table / lay the table.

It does not literally mean cover onto the table in normal English usage, even though the verb historically relates to covering.

Related forms:

• накрывать на стол — to be setting / to set the table habitually
• накрыть на стол — to set the table completely, as a finished action

So in this sentence, the mother asked the speaker to set the table.

Because накрыть на стол is a fixed expression, and it uses на + accusative.

Here:

• стол is accusative singular after на
• на стол is part of the idiom

Compare:

• на стол — onto the table / for the table
• на столе — on the table

In this phrase, Russian does not say накрыть на столе for set the table. The established expression is накрыть на стол.

For the same reason as принесла: the action is viewed as a whole completed task.

The mother asked the speaker to finish setting the table, not merely to be engaged in the process.

So the perfective infinitive накрыть is natural.

If you wanted to focus on process or repeated action, you might see накрывать instead in other contexts.

Because принесла and попросила are two verbs with the same subject:

• мама принесла ... и попросила ...

This is a normal compound predicate / coordination of two actions by one subject, so no comma is needed before и.

A comma would usually appear only if there were a more separate clause structure or extra inserted material requiring it.

Russian word order is fairly flexible, and this sentence could be rearranged without changing the basic meaning.

The given version is natural because it starts with the time expression:

• Перед ужином — before dinner

Then it gives the subject and actions:

• мама принесла поднос с тарелками
• и попросила меня накрыть на стол

This order sounds smooth and narrative.

Other orders are possible, for example:

• Мама перед ужином принесла поднос с тарелками и попросила меня накрыть на стол.

That also works. The difference is mainly one of emphasis and flow, not core meaning.

Yes, that is the most natural interpretation.

Поднос с тарелками means a tray with plates — in other words, the tray had plates on it or was carrying plates.

If Russian wanted to say just a tray and some plates, it would usually be phrased differently.

So the image here is that mom brought a tray loaded with plates or a tray carrying plates.

Yes, but some forms would change:

• Перед ужином мама приносит поднос с тарелками и просит меня накрыть на стол.

That means something like Before dinner, mom brings a tray with plates and asks me to set the table, often as a habitual or narrative present.

But in your original sentence, the past tense plus perfective verbs gives a clear sequence of completed events in the past.