Ночью на море началась буря, и мы закрыли окно в гостинице.

Ночью is the instrumental case of ночь and is commonly used in Russian to express time when something happens.

So:

• ночь = night
• ночью = at night / during the night

This is a very common pattern:

• днём = in the daytime
• вечером = in the evening
• утром = in the morning
• ночью = at night

So Ночью на море началась буря means At night, a storm began at sea / by the sea.

На море literally means on the sea, but in real usage it often means:

• at sea
• by the sea
• at the seaside

The exact English translation depends on context.

In this sentence, на море началась буря most naturally means something like:

• a storm started at sea, or
• a storm began on the sea

Russian often uses на море in places where English would not literally say on the sea.

Compare:

• быть на море = to be at the seaside / at the sea
• отдыхать на море = to vacation by the sea

So this is a normal expression, even if the English equivalent is less literal.

Because the verb here is начаться, not начать.

• начать = to begin something, to start something
• начаться = to begin, to start happening

So:

• Мы начали урок. = We began the lesson.
• Урок начался. = The lesson began.

In your sentence, the subject is буря (storm). The storm is not beginning something else; it is itself beginning. So Russian uses начаться:

• буря началась = the storm began

This is a very common Russian pattern:

• концерт начался = the concert began
• дождь начался = the rain started
• война началась = the war began

There are two things happening there:

1. -л- marks the past tense
2. the ending agrees with the gender of the subject
3. -сь / -ся is the reflexive marker from начаться

The subject is буря, which is feminine singular, so the past tense form must also be feminine:

• masculine: начался
• feminine: началась
• neuter: началось
• plural: начались

So:

• буря началась
• дождь начался
• представление началось
• каникулы начались

Because буря is the subject of the clause.

In Ночью на море началась буря, the thing that began is the storm, so буря is in the nominative:

• буря = subject

Russian past-tense verbs agree with the subject in gender and number, which is why you get началась.

A rough structure is:

• [When?] Ночью
• [Where?] на море
• [What happened?] началась
• [What began? / subject] буря

Even though English usually says A storm began, Russian can place буря after the verb without changing its role as the subject.

Закрыли is the past plural form of закрыть, the perfective verb meaning to close.

Perfective aspect here suggests a completed action:

• мы закрыли окно = we closed the window

This means the action is viewed as a single whole, with a result: the window ended up closed.

Compare:

• закрыли = closed, completed the action
• закрывали = were closing / used to close / closed repeatedly, depending on context

In this sentence, perfective is natural because the storm started, and then we closed the window as a completed response.

It is accusative — but for this noun, the accusative looks the same as the nominative.

Окно is:

• neuter
• inanimate
• singular

For many neuter inanimate nouns in Russian:

• nominative singular = accusative singular

So:

• nominative: окно
• accusative: окно

That is why:

• Мы закрыли окно. = We closed the window.

Compare with a feminine noun where the accusative changes:

• дверь → Мы закрыли дверь.

And with a masculine inanimate noun, it often also stays the same:

• стол → Мы увидели стол.

Because this phrase expresses location, not motion.

• в гостинице = in the hotel
• в гостиницу = into the hotel / to the hotel

Russian uses:

• Prepositional case after в for location
• Accusative case after в for direction or destination

So here:

• окно в гостинице = the window in the hotel

You are not moving into the hotel; you are describing where the window is located.

Compare:

• Мы были в гостинице. = We were in the hotel.
• Мы пошли в гостиницу. = We went to the hotel.

Russian has no articles like a or the.

Whether a noun is understood as definite or indefinite depends on context, word order, and the situation.

So:

• началась буря can mean a storm began or the storm began
• мы закрыли окно can mean we closed the window or a window

In this sentence, English would most naturally say:

• A storm began at sea, and we closed the window in the hotel.

But in a different context, the storm or the window could also be possible.

Russian speakers simply rely on context much more than English speakers do.

Yes, Russian word order is fairly flexible. The sentence could be rearranged, but different orders change the focus or emphasis.

Original:

• Ночью на море началась буря, и мы закрыли окно в гостинице.

This sounds natural and neutral.

Possible variants:

• На море ночью началась буря...
  Slightly different emphasis on at sea
• Буря началась ночью на море...
  Puts буря more upfront
• И мы в гостинице закрыли окно.
  Emphasizes in the hotel

Russian often places new or important information later in the clause. In началась буря, the noun буря comes after the verb, which is a common way to present a new event.

So yes, the order can change, but the original version is very normal and natural.

Because и is joining two separate clauses, each with its own verb:

1. Ночью на море началась буря
2. мы закрыли окно в гостинице

Since these are two independent clauses, Russian normally places a comma before и.

You can think of it as:

• A storm began at sea during the night, and we closed the window in the hotel.

So the comma is not optional here in standard writing.