Я открыл шкаф, чтобы достать тёплый свитер.

In the Russian past tense, verbs agree with the subject in gender and number.

• открыл = masculine singular
• открыла = feminine singular
• открыло = neuter singular
• открыли = plural

So Я открыл tells you the speaker is male. If the speaker were female, it would be Я открыла шкаф...

This is about aspect.

• открыть / открыл = perfective: to open, as a completed action
• открывать / открывал = imperfective: to be opening, to open repeatedly, or to describe the process

In this sentence, the speaker opened the wardrobe/cabinet as one completed action in order to do something next. That makes открыл the natural choice.

So the sentence presents a sequence:

1. I opened the wardrobe
2. to get the sweater

Because чтобы introduces a subordinate clause of purpose.

Russian normally puts a comma before conjunctions like что, чтобы, когда, если when they begin a subordinate clause.

So:

• Я открыл шкаф, чтобы достать тёплый свитер.

The part after the comma explains why the speaker opened the шкаф.

In this sentence, чтобы introduces the purpose of the action.

So:

• Я открыл шкаф = I opened the wardrobe/cabinet
• чтобы достать тёплый свитер = in order to get/take out a warm sweater

A very common pattern is:

• [main action], чтобы + infinitive

when the same person does both actions.

Because the subject is the same for both actions.

The same person:

• opened the wardrobe
• wanted to get the sweater

When the subject stays the same, Russian often uses:

• чтобы + infinitive

Example:

• Я пришёл, чтобы помочь. = I came to help.

If the subject changes, Russian usually uses a finite verb instead:

• Я открыл шкаф, чтобы мама достала свитер.
  = I opened the wardrobe so that Mom could get the sweater.

Again, this is aspect.

• достать = perfective: to get/take out successfully, to obtain the result
• доставать = imperfective: to be taking out, to take out regularly, or to describe the process

Here the purpose is to successfully get one sweater, so достать is natural.

Compare:

• Я открыл шкаф, чтобы достать свитер.
  = I opened the wardrobe to get the sweater.
• Я открывал шкаф и доставал вещи.
  = I was opening the wardrobe and taking things out. / I used to open the wardrobe and take things out.

Not exactly. достать often means something like:

• to get
• to reach
• to take out
• to retrieve

In this context, it suggests getting something from inside the wardrobe/cabinet. So English translations might include:

• to get a warm sweater
• to take out a warm sweater
• to retrieve a warm sweater

It is more specific than simply взять (to take).

Because шкаф is the direct object of открыл, and for a masculine inanimate noun, the accusative singular is the same as the nominative singular.

• nominative: шкаф
• accusative: шкаф

So:

• открыть шкаф = to open a wardrobe/cabinet

If it were a feminine noun, you would often see a clearer change:

• открыть дверь = to open the door
  (дверь looks the same here, but many feminine nouns do change in the accusative, e.g. книга → книгу)

Because свитер is also a direct object here, after достать, and it is masculine singular inanimate.

For masculine inanimate nouns:

• accusative singular = nominative singular

So:

• свитер stays свитер
• the adjective agrees with it, so тёплый also stays in the form that looks like the nominative

That is why you get:

• достать тёплый свитер

If the noun were animate, you would see a different pattern:

• Я увидел нового студента.
  = I saw a new male student.

There, masculine animate accusative looks like the genitive.

Шкаф usually means a large piece of furniture such as:

• wardrobe
• cabinet
• cupboard

Sometimes English translations use closet, depending on context, but шкаф is usually more like a freestanding furniture item than a built-in closet.

So in this sentence, possible translations include:

• wardrobe
• cabinet
• cupboard

The best English word depends on the situation.

ё is pronounced like yo.

So:

• тёплый sounds roughly like TYOP-lyy

A useful fact: in many Russian texts, ё is often written as е, especially in everyday writing and print. So you may also see:

• теплый

But the word is still pronounced тёплый.

For learners, it is helpful to remember that ё is a real letter, not just decoration.

Yes. Russian word order is more flexible than English.

The original sentence is neutral and natural:

• Я открыл шкаф, чтобы достать тёплый свитер.

But you could also say:

• Чтобы достать тёплый свитер, я открыл шкаф.

This puts more emphasis on the purpose first: To get a warm sweater, I opened the wardrobe.

Russian word order often changes for focus, emphasis, or style, but the original version is a very normal default.

Because Russian has no articles.

English says:

• the wardrobe
• a warm sweater

Russian just says:

• шкаф
• тёплый свитер

Whether something means a, the, or just a general noun is understood from context.

So тёплый свитер could mean:

• a warm sweater
• the warm sweater

depending on the situation.