Летом мама замораживает ягоды, чтобы зимой варить компот.

Летом and зимой are adverbial time expressions built from nouns in the instrumental case.

• лето → летом = in summer / during the summer
• зима → зимой = in winter / during the winter

Russian often uses the instrumental this way for seasons and some times of day:

• летом — in summer
• зимой — in winter
• утром — in the morning
• вечером — in the evening

So Летом мама замораживает ягоды... means In summer, Mom freezes berries...

You can also say зимой without a preposition to mean in winter. This is very natural.

Because мама is the subject of the sentence — the person doing the action.

In мама замораживает ягоды:

• мама = the one who freezes
• замораживает = freezes
• ягоды = berries

The subject is normally in the nominative case, so мама stays мама.

Ягоды is the direct object of замораживает — it is the thing being frozen.

The dictionary form is:

• ягода = a berry

Its plural is:

• ягоды = berries

Since this is an inanimate plural noun, the accusative plural looks the same as the nominative plural:

• nominative plural: ягоды
• accusative plural: ягоды

So in this sentence, ягоды means berries as the object of the verb.

In Russian, the present tense of an imperfective verb is often used for habitual or repeated actions.

So мама замораживает ягоды does not have to mean only Mom is freezing berries right now. It can also mean:

• Mom freezes berries
• Mom freezes berries in summer
• Every summer, Mom freezes berries

That is exactly what is happening here: it describes a regular seasonal habit.

The verb замораживать is imperfective, and that fits the meaning well because the sentence describes a repeated, customary action, not one single completed event.

• замораживать = to freeze, to be freezing, to freeze regularly
• заморозить = to freeze completely / to freeze once, as a completed action

Compare:

• Летом мама замораживает ягоды.
  = In summer Mom freezes berries / usually freezes berries.

• Вчера мама заморозила ягоды.
  = Yesterday Mom froze the berries.
  (one completed action)

So the imperfective is chosen because the sentence is about a routine.

Чтобы introduces a purpose clause. It means:

• so that
• in order to

So:

• Летом мама замораживает ягоды, чтобы зимой варить компот.

means:

• In summer Mom freezes berries so that she can make compote in winter.

This is a very common pattern in Russian:

• Я учу русский, чтобы читать книги.
  = I study Russian in order to read books.

• Он пришёл рано, чтобы помочь.
  = He came early to help.

After чтобы, Russian often uses the infinitive when the subject is the same as in the main clause, or when the sentence is expressing a general purpose.

Here the idea is:

• Mom freezes berries in summer
• so that she can cook compote in winter

Since the subject is still мама, Russian naturally uses the infinitive:

• чтобы зимой варить компот

If Russian wanted to state the action with a finite verb, it could use a personal form in some contexts, but the infinitive here is simple and very natural.

Again, this is an aspect question.

• варить = imperfective, to cook/boil, to be making
• сварить = perfective, to cook/make completely, one completed batch

Here the sentence describes a repeated winter activity, not one single finished result:

• чтобы зимой варить компот
  = so that in winter she can make compote / keep making compote

If you said чтобы зимой сварить компот, it would sound more like:

• so that in winter she can make a compote once / a finished compote

That is less natural here, because the whole sentence is about a seasonal habit, not one single occasion.

Компот is a traditional fruit drink common in Russia and many other Slavic-speaking countries. It is made by boiling fruit or berries in water, usually with sugar.

So варить компот literally means something like:

• to boil/cook compote
• more naturally in English: to make compote

A learner may expect a verb like make, but Russian commonly uses варить for foods and drinks that are prepared by boiling.

Because чтобы introduces a subordinate clause, and Russian normally separates such clauses with a comma.

So the structure is:

• main clause: Летом мама замораживает ягоды
• subordinate purpose clause: чтобы зимой варить компот

That is why the comma is required:

• Летом мама замораживает ягоды, чтобы зимой варить компот.

Yes. Russian word order is fairly flexible, because the cases help show each word’s role. This sentence can be rearranged for emphasis.

For example:

• Летом мама замораживает ягоды, чтобы зимой варить компот.
• Мама летом замораживает ягоды, чтобы зимой варить компот.
• Чтобы зимой варить компот, мама летом замораживает ягоды.

All of these are grammatical. The original version is very natural and gives a nice time contrast:

• Летом ... зимой

That makes the sentence easy to follow.

Russian has no articles like a or the. So зимой simply means in winter or in the winter, depending on context.

English translation depends on style:

• in winter sounds more general
• in the winter can also work in some contexts

Russian itself does not mark that distinction with an article.

It is completely normal. Russian often puts time expressions near the beginning of the sentence, especially when setting the scene.

So:

• Летом мама замораживает ягоды...

feels very natural, like:

• In summer, Mom freezes berries...

Starting with летом helps frame the contrast with зимой later in the sentence. It makes the seasonal logic especially clear:

• in summer → freeze berries
• in winter → make compote