На ужин мама жарит картошку с луком.

На ужин means for dinner.

Here на + accusative is used in a very common Russian pattern to mean for a meal / for an occasion:

• на завтрак — for breakfast
• на обед — for lunch
• на ужин — for dinner

So На ужин мама жарит картошку с луком is literally something like For dinner, Mom is frying potatoes with onion.

Starting the sentence with На ужин puts the focus on what this is for. Russian word order is flexible, so this part can be moved to the front for emphasis.

Because after на Russian can take different cases depending on the meaning.

Here на ужин uses the accusative case and means for dinner.

Compare:

• на ужин — for dinner
• на ужине — at dinner / at the dinner event

So in this sentence, the idea is purpose: Mom is cooking this for dinner, not that she is doing it at dinner.

Because it is the direct object of жарит.

The verb жарить means to fry, and the thing being fried goes into the accusative case.
картошка is a feminine noun ending in -а, so in the accusative singular it becomes -у:

• nominative: картошка
• accusative: картошку

So:

• мама жарит картошку — Mom is frying potatoes

This is very natural in Russian.

Картошка often works like a mass noun or the name of a dish/food, so singular is very common even when English would use a plural:

• есть картошку — to eat potatoes
• жарить картошку — to fry potatoes

Russian is treating it more like potato as food material, not necessarily counting individual potatoes.

You can think of it like English chicken, fish, or rice in some contexts.

Both refer to potato, but the style is different.

• картошка — common, everyday, conversational
• картофель — more formal, neutral, dictionary-style, or technical

In ordinary family speech, картошка is much more natural here. Since the sentence has мама, the casual everyday word fits perfectly.

Because с meaning with requires the instrumental case.

The noun лук becomes луком in the instrumental singular:

• nominative: лук
• instrumental: луком

So:

• с луком — with onion

This is a very common pattern:

• с сыром — with cheese
• с мясом — with meat
• с маслом — with butter

Here it clearly means onion.

Russian лук can mean:

• onion
• bow (the weapon)

But in food contexts like картошка с луком, it can only mean onion.

Жарит is imperfective, while пожарит is perfective.

• жарить / жарит — process, repeated action, or general present
• пожарить / пожарит — completed action in the future

In this sentence, жарит fits because it can mean either:

• Mom is frying potatoes with onions right now, or
• Mom fries potatoes with onions / is making potatoes with onions for dinner

If you said мама пожарит картошку с луком, that would mean Mom will fry potatoes with onions.

It can mean both, depending on context.

Russian present-tense imperfective verbs often cover both:

• an action happening right now
• a habitual or regular action

So мама жарит картошку с луком could mean:

• Mom is frying potatoes with onions
• Mom fries potatoes with onions

In this sentence, many people would understand it as something happening now, especially because of the cooking context.

Usually yes, but not always in a narrow technical sense.

Жарить generally means cooking in a pan, in fat/oil, or by frying/roasting heat. In everyday translation, to fry is the best match.

So жарит картошку is very naturally fries potatoes or is frying potatoes.

Because Russian word order is flexible.

The neutral order would often be:

• Мама жарит картошку с луком на ужин.

But putting На ужин first makes for dinner the starting point or topic:

• На ужин мама жарит картошку с луком.

This sounds natural and may answer an implied question like What is Mom making for dinner?

Russian word order often shows focus and information structure, not just grammar.

Yes. That is also grammatical and natural.

All of these are possible:

• На ужин мама жарит картошку с луком.
• Мама жарит картошку с луком на ужин.
• Мама на ужин жарит картошку с луком.

The basic meaning stays the same, but the emphasis shifts a little.
The original sentence emphasizes for dinner first.

Because Russian has no articles.

So Russian does not normally distinguish with separate words between:

• Mom is frying potatoes
• Mom is frying the potatoes
• Mom is frying some potatoes

The exact meaning depends on context.

That is why мама жарит картошку с луком has no article words at all.

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

It is the person doing the action:

• мама — Mom
• жарит — is frying / fries

So мама is the one who fries the potatoes.

Yes. Мама is a regular feminine noun in -а.

Its forms behave like a standard feminine noun:

• nominative: мама
• accusative: маму
• instrumental: мамой

In this sentence it stays мама because it is the subject.

The stress is:

На у́жин ма́ма жа́рит карто́шку с лу́ком.

Word by word:

• на
• у́жин
• ма́ма
• жа́рит
• карто́шку
• с лу́ком

A rough pronunciation guide:

• Na OO-zhin MA-ma ZHA-rit kar-TOHSH-koo s LOO-kam

A few notes:

• ж sounds like the s in measure
• unstressed о is often pronounced closer to a in natural speech
• с луком is pronounced smoothly together

Yes, and in cooking that is exactly how it works.

с луком literally means with onion, but in food language it usually means the dish is prepared with onion as an ingredient.

So картошку с луком means potatoes cooked together with onion, not just potatoes physically next to an onion.

Grammatically, с луком is singular: with onion.

But in Russian food descriptions, singular often refers to the ingredient in a general way, not necessarily to the exact number of pieces.

So it does not strongly focus on counting onions. It just means onion is part of the dish.

Not normally in this meaning.

с луками would be instrumental plural and would sound wrong here for ordinary cooking. Russian normally says:

• картошка с луком — potatoes with onion

The singular is the standard way to name the ingredient.

Yes, completely.

Russian often uses a noun directly as the subject without needing a pronoun:

• мама жарит... — Mom is frying...
• она жарит... — She is frying...

Using мама is enough, and adding она would usually be unnecessary unless you want contrast or emphasis.

Yes, it can.

Because жарит is imperfective present, the sentence can describe:

• what is happening now
• what she generally does
• what is being made on this occasion

If context suggests a routine, it can mean something like:

• Mom makes potatoes with onions for dinner

If context is immediate, it more likely means:

• Mom is frying potatoes with onions for dinner