Аварийная служба работает ночью.

Because аварийная is an adjective modifying служба.

• служба is a feminine singular noun.
• Russian adjectives must agree with the noun they describe in gender, number, and case.

So:

• masculine: аварийный
• feminine: аварийная
• neuter: аварийное
• plural: аварийные

Here, since служба is feminine singular, we get аварийная служба.

It means something like emergency service, emergency repair service, or breakdown service, depending on context.

The adjective аварийный / аварийная comes from авария, which can mean:

• accident
• breakdown
• emergency situation

And служба often means:

• service
• department
• unit
• agency

So аварийная служба is not just any service; it is a service that deals with emergencies, breakdowns, or urgent repairs.

Because the subject is singular.

• аварийная служба = one service
• therefore the verb must also be singular: работает = works / is operating

Compare:

• Аварийная служба работает. = The emergency service works / is operating.
• Аварийные службы работают. = Emergency services work / are operating.

Ночью is the correct form for at night.

It is the instrumental singular form of ночь. In Russian, some time expressions use the instrumental case without a preposition to mean during a certain part of the day.

Examples:

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

So:

• ночь = night
• ночью = at night

Because Russian often uses the instrumental case by itself for certain time expressions.

In English, you say at night, but Russian does not need a separate word for at here. The case ending already does that job.

So:

• работает ночью = works at night

This is a very common pattern, especially with parts of the day.

It can mean either, depending on context, but in this sentence it most naturally means a general fact or schedule:

• The emergency service operates at night.
• The emergency service works at night.

Russian present tense often covers both:

• what is happening now
• what happens regularly
• what is generally true

Without extra context, this sentence sounds like a general statement about when the service is available.

Yes. Russian word order is more flexible than English because the grammatical endings carry a lot of information.

The neutral order here is:

• Аварийная служба работает ночью.

But you could also say:

• Ночью работает аварийная служба.
• Работает ночью аварийная служба.

These versions are grammatically possible, but the emphasis changes:

• starting with ночью emphasizes at night
• starting with работает can sound more marked or context-driven

For a learner, the original version is the safest and most neutral.

Russian does not have articles like the or a/an.

So аварийная служба can mean:

• the emergency service
• an emergency service
• sometimes just emergency service

The exact meaning depends on context.

For example:

• if both speakers know which service is meant, English would usually say the
• if it is being mentioned more generally, English might say an or no article-like phrase depending on style

No, they are related to the idea of work, but they are different words.

• работа = work, job
• служба = service, department, agency, duty

In this sentence, служба means an organized service or department, not the abstract idea of work.

So аварийная служба is not emergency work; it is an emergency service/unit.

The stress is:

• авари́йная
• слу́жба
• рабо́тает
• но́чью

So the sentence is pronounced roughly like:

• avarEEynaya SLOOZHba raBOtaet NOCHyu

A few pronunciation notes:

• жб in служба can be a little tricky; say it smoothly.
• чью in ночью sounds like chyu.
• Stress is very important in Russian, so it is worth learning these stressed syllables early.