Перед тем как готовить ужин, стоит разморозить рыбу.

Перед тем как is a fixed expression meaning before when it introduces a clause.

• перед = before / in front of
• тем = that / that thing, in instrumental case here
• как = how / as

Together, перед тем как means before doing something / before someone does something.

You cannot normally say перед как in standard Russian. The тем is part of the usual construction.

Examples:

• Перед тем как уйти, выключи свет. — Before leaving, turn off the light.
• Перед тем как мы поедем, позвони. — Before we go, call.

After перед тем как, Russian can use an infinitive when the subject is general or understood from context.

So:

• Перед тем как готовить ужин... = Before preparing dinner...

This works like English before preparing dinner or before you prepare dinner, depending on context.

If you want to state the subject clearly, you can use a full clause:

• Перед тем как ты будешь готовить ужин, стоит разморозить рыбу.
• Перед тем как мы будем готовить ужин, стоит разморозить рыбу.

The infinitive version is more compact and very natural.

Here стоит does not mean costs. It means:

• it is worth
• it is advisable
• one should / it’s a good idea to

So стоит разморозить рыбу means something like:

• it’s worth thawing the fish
• you should thaw the fish
• it’s a good idea to thaw the fish

This is a common impersonal construction:

• Стоит подождать. — It’s worth waiting. / You should wait.
• Стоит проверить. — It’s worth checking.

It sounds softer and less direct than a command.

This is about aspect, which is very important in Russian.

готовить — imperfective

It describes the process/activity of cooking, without focusing on completion:

• готовить ужин = to cook dinner / to be preparing dinner

In перед тем как готовить ужин, the idea is before starting or engaging in the activity of cooking dinner, so the imperfective is natural.

разморозить — perfective

It focuses on the result: the fish becomes thawed.

• размораживать = to be thawing / thaw repeatedly
• разморозить = to thaw completely, to get it thawed

Since the sentence means you should complete that action first, the perfective is used:

• стоит разморозить рыбу = it’s a good idea to thaw the fish first / get the fish thawed

So the contrast is very natural:

• before doing the activity → imperfective
• it is advisable to complete this preparatory action → perfective

Because рыбу is the accusative case, used for the direct object of the verb.

The verb разморозить takes a direct object:

• thaw what? → рыбу

Forms:

• nominative: рыба — fish
• accusative: рыбу — fish (as the object)

Compare:

• Рыба лежит на столе. — The fish is lying on the table.
  Here рыба is the subject.
• Я разморозил рыбу. — I thawed the fish.
  Here рыбу is the object.

The comma separates the introductory subordinate clause from the main clause.

Structure:

• Перед тем как готовить ужин = subordinate clause
• стоит разморозить рыбу = main clause

So Russian punctuation requires:

• Перед тем как готовить ужин, стоит разморозить рыбу.

This is similar to English:

• Before cooking dinner, it’s worth thawing the fish.

No, Перед как... is not standard Russian.

You normally need:

• перед тем как

In some contexts, Russian can use other ways to say before, for example:

• Перед приготовлением ужина... — Before the preparation of dinner...
• Прежде чем готовить ужин... — Before cooking dinner...

But перед как is not the normal pattern.

Both can mean before, but they are a little different in style and structure.

перед тем как

Very common, neutral, conversational and written.

• Перед тем как готовить ужин, стоит разморозить рыбу.

прежде чем

Also common, often a bit more formal or bookish, though still very natural.

• Прежде чем готовить ужин, стоит разморозить рыбу.

In many sentences they are interchangeable. A learner can safely use both, but перед тем как often feels a bit more everyday and transparent.

Yes. Russian often allows a noun phrase instead of a verbal clause.

For example:

• Перед приготовлением ужина стоит разморозить рыбу.

This means essentially the same thing:

• Before preparing dinner, it’s worth thawing the fish.

Compare the styles:

• Перед тем как готовить ужин...
  more verbal, more action-focused, very natural in speech

• Перед приготовлением ужина...
  slightly more formal or compact, common in written language

Both are correct.

Yes, the subject is general or understood from context.

Russian often leaves the subject unstated when it means:

• you
• one
• we
• whoever is involved in the situation

So this sentence can mean:

• before you cook dinner, you should thaw the fish
• before we cook dinner, it’s worth thawing the fish
• before cooking dinner, one should thaw the fish

The sentence is intentionally impersonal and general.

Russian has no articles like a or the.

So ужин can mean:

• dinner
• the dinner
• a dinner

You understand the exact meaning from context.

In this sentence, готовить ужин is a very standard phrase meaning to cook dinner. English usually also says simply cook dinner, without an article.

Yes, Russian word order is flexible, though some orders sound more neutral than others.

The original:

• Перед тем как готовить ужин, стоит разморозить рыбу.

This is neutral and natural.

You could also say:

• Рыбу стоит разморозить перед тем как готовить ужин.
• Стоит разморозить рыбу перед тем как готовить ужин.

These versions are also grammatical. The difference is mainly in emphasis:

• starting with Перед тем как... emphasizes the time relationship
• starting with рыбу highlights the fish
• starting with стоит разморозить emphasizes the recommendation

For learners, the original order is a very good default.

Yes, but the nuance changes.

• Стоит разморозить рыбу.
  = It’s worth thawing the fish. / It’s a good idea to thaw the fish.
  Softer, more like advice.

• Надо разморозить рыбу.
  = It is necessary to thaw the fish. / You need to thaw the fish.
  Stronger, more direct.

• Нужно разморозить рыбу.
  Similar to надо, also common.

So стоит sounds more like a recommendation, while надо / нужно sounds more like necessity.

Yes. It is built from the idea of cold/frost.

• мороз = frost
• морозить = to freeze
• заморозить = to freeze
• разморозить = to unfreeze / defrost / thaw

The prefix раз- often gives a sense of undoing or reversing a state, so разморозить means to reverse freezing.

Its imperfective partner is:

• размораживать = to be thawing / to thaw repeatedly

So:

• Я разморозил рыбу. — I thawed the fish.
• Я размораживал рыбу. — I was thawing the fish / I used to thaw fish.