Будучи студентом, он работал ночью.

Будучи is a special form of the verb быть (to be). It is a gerund (in Russian grammar, деепричастие), and here it means something like:

• being
• while being
• when he was

So Будучи студентом, он работал ночью literally feels like:

• Being a student, he worked at night
• more naturally: While he was a student, he worked at night

This form is quite common in written Russian, but it is usually more formal than everyday speech.

Because after быть in this kind of structure, Russian often uses the instrumental case for a role, profession, or status.

So:

• студент = nominative
• студентом = instrumental

Here, будучи студентом means being a student.

This is the same pattern you see in sentences like:

• Он был студентом. = He was a student.
• Она стала врачом. = She became a doctor.

So студентом is not random: it shows the state or role the person had.

Because будучи студентом is a gerund phrase (деепричастный оборот), and such phrases are normally set off with commas in Russian.

So:

• Будучи студентом, он работал ночью.

The comma marks the extra circumstance: while being a student.

Compare:

• Читая книгу, он пил чай. = While reading a book, he drank tea.
• Будучи студентом, он работал ночью.

This punctuation is standard.

Yes. The subject of the main action and the subject of будучи must be the same.

In this sentence:

• он работал = he worked
• будучи студентом = being a student

So the person who was a student is the same person who worked at night: he.

This is an important rule with Russian gerunds: the implied subject of the gerund should match the subject of the main verb.

It is understandable and correct, but it often sounds a bit more bookish, formal, or written than the most natural everyday spoken version.

A more conversational way to say the same idea might be:

• Когда он был студентом, он работал ночью.
• Он работал ночью, когда был студентом.

So будучи студентом is good Russian, but many speakers would choose a clause with когда in casual speech.

Yes, but the most natural English translation is usually:

• When he was a student, he worked at night.
• While he was a student, he worked at night.

A very literal translation, Being a student, he worked at night, is possible, but it sounds less natural in modern English.

So the Russian structure is compact, but English usually prefers a full clause.

Because the sentence refers to a past period in his life.

• работал = worked / was working

The sentence gives background information:

• Будучи студентом = during the time when he was a student
• он работал ночью = he worked at night

Russian past tense does not itself distinguish sharply between worked and was working in the way English often does. The exact nuance depends on context.

Ночью means at night or during the night.

It is a very common adverbial form.

Here are the differences:

• ночью = at night
• по ночам = at nights / night after night / regularly at night
• в ночь usually means on the night of or forms part of another expression, so it does not fit as well here

In this sentence, ночью is a natural way to say when he worked.

If you said по ночам, it would emphasize habitual repetition even more strongly:

• Будучи студентом, он работал по ночам.
  = When he was a student, he used to work at nights.

Yes. Russian word order is flexible, and several versions are possible:

• Будучи студентом, он работал ночью.
• Он, будучи студентом, работал ночью.
• Он работал ночью, будучи студентом.

All are grammatical, but they differ slightly in focus and style.

The original version puts the background condition first:

• Будучи студентом = setting the scene first

That is a very natural choice in writing.

Yes. Работал is imperfective, and that fits well here because it describes an ongoing or repeated activity in the past.

• работал = worked / was working / used to work

If you used проработал, the meaning would change. Проработал is perfective and usually suggests a completed stretch of time, often with a duration:

• Он проработал всю ночь. = He worked the whole night through.
• Он проработал там три года. = He worked there for three years.

In your sentence, the point is simply that during his student years, he worked at night, so работал is the natural choice.

Yes. Будучи is often used with nouns or adjectives to describe someone’s state, role, or condition:

• Будучи ребёнком, он жил в деревне. = When he was a child, he lived in a village.
• Будучи врачом, она понимала риск. = Being a doctor, she understood the risk.
• Будучи занятым, он не ответил сразу. = Being busy, he didn’t answer right away.

With nouns denoting identity or role, the following noun is often in the instrumental case:

• ребёнком
• врачом
• студентом

Yes, sometimes, especially if the subject is clear from context:

• Будучи студентом, работал ночью.

But in a standalone sentence, keeping он is more normal and clearer:

• Будучи студентом, он работал ночью.

Russian can drop subjects more easily than English in some contexts, but not as freely as languages like Spanish or Italian. If there is no context, the pronoun often stays.

It most naturally suggests a repeated or ongoing situation during the time he was a student.

So the idea is:

• during his student years
• he worked at night

Because работал is imperfective, it often gives that background/habitual sense.

Depending on context, English might translate it as:

• When he was a student, he worked at night.
• When he was a student, he used to work at night.

Both can work.