Когда хор поёт тихо, дирижёр двигает руками очень спокойно.

Because хор is grammatically singular in Russian. It means choir, which is a group made up of many people, but Russian treats it as one unit.

So:

• хор поёт = the choir sings
• певцы поют = the singers sing

This is similar to English the choir sings, where the verb is often singular too.

Here когда means when.

It introduces a subordinate clause:

• Когда хор поёт тихо = When the choir sings quietly
• дирижёр двигает руками очень спокойно = the conductor moves his hands very calmly

In a sentence like this, когда can describe a general situation or repeated/habitual action, not only one specific moment.

Because Когда хор поёт тихо is a subordinate clause introduced by когда, and in Russian subordinate clauses are normally separated from the main clause with a comma.

So:

• Когда хор поёт тихо, дирижёр двигает руками очень спокойно.

The comma would still be needed if the clause came second:

• Дирижёр двигает руками очень спокойно, когда хор поёт тихо.

Because they are adverbs.

In Russian, many adverbs are formed from adjectives and often end in -о:

• тихий → тихо = quiet → quietly
• спокойный → спокойно = calm → calmly

Here they describe how something happens:

• поёт тихо = sings quietly
• двигает руками спокойно = moves his hands calmly

They describe different things:

• тихо refers to low volume or softness of sound

  • хор поёт тихо = the choir sings quietly / softly

• спокойно refers to manner, emotional tone, or smoothness

  • дирижёр двигает руками спокойно = the conductor moves his hands calmly

So even though both can sound similar in English, they are not interchangeable here.

Yes. Очень means very, and it can modify:

• adjectives: очень тихий = very quiet
• adverbs: очень тихо, очень спокойно = very quietly, very calmly

So:

• спокойно = calmly
• очень спокойно = very calmly

This is completely normal Russian.

Because Russian often uses the instrumental case for the body part or means by which an action is performed.

руками is the instrumental plural of руки:

• nominative plural: руки
• instrumental plural: руками

So двигать руками literally means something like to move with the hands or to move one’s hands.

This is a very common pattern in Russian:

• махать руками = wave one’s hands
• пожать плечами = shrug one’s shoulders
• кивать головой = nod one’s head

English often uses a direct object here, but Russian frequently prefers instrumental with body parts.

Because in Russian, with many body-part expressions, the natural structure is not a direct object but an instrumental phrase.

So:

• двигает руками = moves his hands / moves with his hands

If you said двигает руки, it would sound much less natural in this context. A Russian speaker normally says двигать руками when talking about the general action of moving one’s hands.

Because the sentence describes an ongoing or repeated manner of action, not a single completed movement.

Двигать is imperfective, so двигает means:

• is moving
• moves
• tends to move

That fits well with a general description like this:

• when the choir sings quietly, the conductor moves his hands very calmly

A perfective verb would suggest a single completed action, which is not the point here.

Not necessarily. In Russian, the present tense can describe:

• what is happening now
• what usually happens
• a general rule or typical situation

Here it most naturally sounds like a general description:

• whenever the choir sings quietly, the conductor moves his hands very calmly

So the present tense is being used in a broad, habitual sense.

Yes. Russian word order is fairly flexible, though the most neutral version is the one you were given.

For example, these are also possible:

• Когда хор тихо поёт, дирижёр двигает руками очень спокойно.
• Дирижёр очень спокойно двигает руками, когда хор поёт тихо.

The meaning stays basically the same, but the emphasis changes slightly.

Russian often moves words around for rhythm, focus, or style more freely than English.

Yes, it is important for pronunciation and stress.

Поёт is pronounced roughly pa-YOT. The ё tells you:

• the sound is yo
• the stress falls there

So:

• поёт = sings
• not поет with a plain e sound

In printed Russian, ё is sometimes written as е, but learners should remember the correct form is поёт. The same is true for дирижёр.

The main thing is that it is a masculine singular noun, so the verb agrees with it:

• дирижёр двигает

Also, the ё matters in pronunciation:

• дирижёр is stressed on the last syllable

So this part is straightforward:

• singular subject дирижёр
• singular verb двигает

Sometimes, yes, depending on context.

In this sentence, когда most directly means when, but in natural English the idea can overlap a little with while, because two actions are happening together:

• the choir sings quietly
• the conductor moves his hands calmly

Still, for grammar purposes, когда is the normal Russian word for when here. If you want to think of it as when first, that is the safest choice.