На следующий день остался плов, и мама ещё пожарила котлеты из говядины.

In Russian, на следующий день is a very common expression meaning the next day / on the following day.

Here, на + accusative is used in a set time expression.
A literal breakdown is something like on the next day.

Using в следующий день would sound unnatural in standard Russian for this meaning. Russian usually says:

• на следующий день = the next day
• в тот день = on that day

So this is something you should mostly learn as a fixed phrase.

Because it agrees with день.

In на следующий день:

• день is masculine singular
• after на in this time expression, день is in the accusative
• for an inanimate masculine noun, the accusative looks the same as the nominative

So:

• nominative: следующий день
• accusative: на следующий день

That is why the adjective stays следующий, not следующего.

Both are possible.

Russian word order is flexible, and changing the order changes the focus a little.

• Остался плов puts more attention on the fact of what was left
• Плов остался sounds more neutral or puts more focus on плов

In this sentence, остался плов can sound natural because it introduces what remained after the previous meal.

So this is not a grammar issue but a matter of information structure and emphasis.

Because the subject is плов, which is:

• masculine
• singular

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

• остался = masculine singular
• осталась = feminine singular
• осталось = neuter singular
• остались = plural

Since плов is masculine singular, the verb must be остался.

Остался means remained / was left over.

So остался плов is not just there was pilaf. It specifically means that some pilaf was still there from before, or was left after an earlier meal.

That gives a stronger sense of leftover food than был would.

Compare:

• был плов = there was pilaf
• остался плов = there was pilaf left / some pilaf remained

Пожарила is a perfective verb, while жарила is imperfective.

Here the speaker is talking about a completed action: the mother fried/cooked the cutlets, and the action is presented as a finished event.

• жарила = was frying / used to fry / fried (with process emphasis)
• пожарила = fried, cooked up (completed result)

In a simple narrative about what happened next, Russian often prefers the perfective form:

• мама ещё пожарила котлеты = and мама also cooked/fried some cutlets

Here ещё means something like:

• also
• in addition
• besides that

So the idea is:

• there was still pilaf left,
• and on top of that, мама cooked some beef cutlets too.

Be careful: ещё can mean different things in different contexts, such as still, yet, or more.
In this sentence, it has the sense of additionally.

Because из + genitive is commonly used to mean made from a material or ingredient.

So:

• котлеты из говядины = cutlets made from beef

The noun говядина becomes genitive after из:

• nominative: говядина
• genitive: говядины

This is very common in Russian:

• суп из курицы = soup made from chicken
• сок из яблок = juice made from apples
• дом из дерева = house made of wood

Not exactly.

Russian котлеты are often pan-fried minced-meat patties, closer in many cases to:

• meat patties
• croquettes
• sometimes even small burgers, depending on context

So you should not always imagine a thin breaded cutlet in the English sense.

In котлеты из говядины, the image is usually beef patties made from ground beef.

Russian has no articles.

So плов can mean:

• pilaf
• the pilaf
• some pilaf

The exact meaning comes from context. Here, because of остался, the natural interpretation is some pilaf was left or the pilaf was left over.

English needs an article or determiner, but Russian does not.

Yes, that is the literal structure, but it sounds unnatural in normal English.

Russian often uses verbs like остаться where English would prefer a phrase like:

• there was some pilaf left
• some pilaf remained

So the Russian grammar is straightforward, but the most natural English translation usually has to be adjusted.

Normally, no.

In Russian, мама is usually written with a lowercase letter unless it begins the sentence. Even when it means Mom, it is not usually capitalized the way English sometimes capitalizes family titles used as names.

So:

• мама пришла
• папа сказал

are normal.

Russian often leaves that idea unspoken.

In English, we often say:

• some pilaf
• some cutlets

In Russian, the bare noun is often enough:

• остался плов
• пожарила котлеты

If needed, Russian can add words like:

• немного плова = a little pilaf
• какие-то котлеты = some cutlets

But in this sentence, context already makes the quantity non-specific, so no extra word is necessary.