На ужин мы заказали плов с говядиной, а моя подруга — пюре со свининой.

На ужин is the standard Russian way to mean for dinner / at dinner in this kind of sentence.

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

So На ужин мы заказали... means For dinner, we ordered...

Для ужина is grammatically possible in some contexts, but it usually sounds more like for the purpose of dinner or intended for dinner, not the normal idiomatic way to say what someone ate or ordered at dinner.

Because the subject is мы = we.

Russian past tense agrees with the subject in gender and number:

• я заказал = I ordered (male speaker)
• я заказала = I ordered (female speaker)
• мы заказали = we ordered

So:

• мы заказали плов с говядиной = we ordered pilaf with beef

The dash shows that the verb is omitted because it is understood from the first part.

Full version:

• На ужин мы заказали плов с говядиной, а моя подруга заказала пюре со свининой.

Natural shortened version:

• На ужин мы заказали плов с говядиной, а моя подруга — пюре со свининой.

This is very common in Russian. English does something similar:

• We ordered pilaf with beef, and my friend — mashed potatoes with pork.

In smoother English, we would usually repeat the verb, but in Russian the omission is very normal.

А often marks a contrast or comparison, even when the meaning is not strongly but.

Here the sentence compares what we ordered with what my friend ordered:

• мы заказали...
• а моя подруга...

So а is a very natural choice because it means something like:

• while
• whereas
• and as for

It is not a strong contradiction like но = but, but it does set the two choices against each other.

Плов is in the accusative case because it is the direct object of заказали.

We ask:

• Что мы заказали? = What did we order?
• Плов.

Because плов is an inanimate masculine noun, its accusative singular is the same as its nominative singular:

• nominative: плов
• accusative: плов

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

They are in the instrumental case because after с / со meaning with, Russian normally uses the instrumental.

• с говядиной = with beef
• со свининой = with pork

Base forms:

• говядина → говядиной
• свинина → свининой

This is a very useful pattern:

• чай с лимоном = tea with lemon
• суп с курицей = soup with chicken
• рис с овощами = rice with vegetables

Both с and со mean with here. Russian uses со instead of с in some places to make pronunciation easier.

That is why you get:

• с говядиной
• со свининой

The cluster ссв... would be awkward, so Russian uses со before свининой.

This happens in other expressions too, for example:

• со мной = with me
• со стола = from the table

So the difference is mostly phonetic, not grammatical.

Пюре is also the direct object, so functionally it is in the accusative.

However, пюре is an indeclinable noun, which means its form does not change across cases in normal usage.

So:

• nominative: пюре
• accusative: пюре
• after many prepositions: still пюре

This is common with some borrowed nouns in Russian.

Also, in everyday Russian пюре usually means mashed potatoes.

Because моя подруга is the subject of the second clause.

The full sentence is understood as:

• а моя подруга заказала пюре со свининой

Here моя подруга is the person doing the action, so it must be in the nominative:

• моя подруга = my female friend

Yes. Russian word order is flexible, and different orders change emphasis more than basic meaning.

The given sentence:

• На ужин мы заказали плов с говядиной, а моя подруга — пюре со свининой.

This sounds natural and topical: as for dinner, we ordered...

Other possible versions include:

• Мы на ужин заказали плов с говядиной, а моя подруга — пюре со свининой.
• Плов с говядиной мы заказали на ужин, а моя подруга — пюре со свининой.

These are all grammatical, but the original is a very normal neutral way to present the information.

They are close in meaning, but not exactly identical in feel.

• плов с говядиной = pilaf with beef
• говяжий плов = beef pilaf

The с + instrumental pattern is very common for dishes and ingredients, especially in menus and everyday speech. It clearly presents the dish plus what it comes with.

Similarly:

• пельмени с мясом
• блины с творогом
• картошка с грибами

So плов с говядиной sounds very natural.

Yes. Подруга means a female friend.

So моя подруга means:

• my female friend or
• my girlfriend in some contexts, depending on the situation

If you wanted male friend, you would say:

• мой друг

Here the feminine possessive моя matches the feminine noun подруга.

Russian often omits repeated words when they are easy to understand from context. This makes the sentence more concise and natural.

So instead of:

• ...а моя подруга заказала пюре со свининой

Russian can say:

• ...а моя подруга — пюре со свининой

This kind of ellipsis is especially common in comparisons and parallel structures.

Говядина and свинина are the names of the meats:

• говядина = beef
• свинина = pork

They are not the animals themselves.

Compare:

• корова = cow
• свинья = pig

Just like English distinguishes cow vs beef and pig vs pork, Russian also has separate words.

So:

• плов с говядиной = pilaf with beef
• пюре со свининой = mashed potatoes with pork