Перед ужином стоит разморозить рыбу, если в морозилке больше ничего нет.

It comes from the verb стоить, which often means to cost, but in the pattern стоит + infinitive it means it is worth doing or it would be a good idea to.

So стоит разморозить рыбу means something like:

• it’s worth defrosting the fish
• you should defrost the fish
• it would be a good idea to defrost the fish

This is softer and less direct than надо or нужно.

Russian often leaves the subject unstated in general advice sentences.

Here, стоит разморозить рыбу is an impersonal-style recommendation. The understood subject is something like you, we, or one, depending on context.

English often has to add a subject, but Russian does not always need one.

This is about aspect.

• разморозить = perfective
• размораживать = imperfective

The perfective verb is used because the sentence is talking about a single completed result: the fish should get thawed before dinner.

So the focus is not on the process of thawing, but on the completed action.
If you used размораживать, it would sound more like a process, habit, or ongoing action.

Рыбу is the accusative singular of рыба.

It is in the accusative because it is the direct object of разморозить: the action is being done to the fish.

• dictionary form: рыба
• accusative singular: рыбу

For feminine nouns ending in -а, this change to -у in the accusative singular is very common.

Because the preposition перед requires the instrumental case.

So:

• ужин = nominative
• ужином = instrumental

That gives:

• перед ужином = before dinner

This is a general rule:

• перед домом = in front of the house
• перед встречей = before the meeting
• перед ужином = before dinner

No. Перед can be used both for:

• space: перед домом = in front of the house
• time: перед ужином = before dinner

So in this sentence it is a time expression, not a physical one.

В морозилке means in the freezer.

Here в is used with the prepositional case because it describes location.

• dictionary form: морозилка
• prepositional singular: в морозилке

So the ending changes because the noun is after в in a location meaning.

Also, морозилка is a common everyday word. You may also hear more formal words like морозильник or морозильная камера.

Here больше does not simply mean more in a mathematical sense.

In negative sentences, больше often means:

• else
• any more
• any longer

So в морозилке больше ничего нет means:

• there is nothing else in the freezer
• there is nothing more left in the freezer

It gives the idea that the freezer has no other available food.

In Russian, this is completely normal. Russian uses negative concord, which means multiple negative words appear together in the same sentence.

So:

• ничего нет = there is nothing
• никого не вижу = I see nobody
• никогда не был = I have never been

This is standard Russian grammar, not a mistake.

Because нет requires the genitive case.

• ничто is the nominative form
• ничего is the genitive form

After нет, Russian asks effectively нет чего? = there is none of what?

So:

• ничего нет = there is nothing

The same thing happens with regular nouns:

• молока нет = there is no milk
• времени нет = there is no time

Нет is the normal Russian way to say there is no / there are no in the present.

So:

• в морозилке ничего нет = there is nothing in the freezer

Russian usually does not use a present-tense form like English there is. In negative existence sentences, нет is the standard form.

Because если introduces a subordinate clause.

Russian normally puts a comma before clauses introduced by words like:

• если = if
• когда = when
• потому что = because
• что = that

So the comma in ..., если в морозилке больше ничего нет is required.

Yes. Russian word order is flexible.

For example, you could also say:

Если в морозилке больше ничего нет, перед ужином стоит разморозить рыбу.

That is still grammatical. The original version starts with перед ужином, which puts a little more focus on when the action should happen.

Russian does not have articles like the and a, so рыбу can mean either the fish or a fish, depending on context.

In this sentence, the context suggests some fish that is available to be used for dinner, so English often translates it as the fish. But Russian itself does not mark that distinction with an article.

No. Стоит is usually softer.

Compare:

• стоит разморозить рыбу = it would be a good idea to defrost the fish
• нужно разморозить рыбу = it is necessary to defrost the fish
• надо разморозить рыбу = you need to defrost the fish

So стоит sounds more like advice or a sensible suggestion than a strict necessity.