Моя подруга играет на флейте, а её брат — на барабане.

Because подруга is a feminine noun, and the possessive my has to agree with it in gender, number, and case.

• мой = my (masculine singular)
• моя = my (feminine singular)
• моё = my (neuter singular)
• мои = my (plural)

So:

• мой брат = my brother
• моя подруга = my female friend

Here, both words are in the nominative singular, because моя подруга is the subject of the sentence.

Usually, подруга means female friend, not necessarily a romantic girlfriend.

This is a very common point for English speakers because English girlfriend can mean either:

• a female friend, or
• a romantic partner

In Russian:

• подруга usually means female friend
• девушка can mean girlfriend in the romantic sense, depending on context

So in this sentence, моя подруга is normally understood as my female friend.

Играет is the 3rd person singular form of играть (to play).

The subject is моя подруга, which is:

• third person = she
• singular = one person

So the verb must match:

• я играю = I play
• ты играешь = you play
• он / она играет = he / she plays
• мы играем = we play
• вы играете = you play
• они играют = they play

So:

• Моя подруга играет = My friend plays

Because Russian normally says играть на + instrument, literally something like to play on an instrument.

Examples:

• играть на пианино = to play the piano
• играть на гитаре = to play the guitar
• играть на скрипке = to play the violin
• играть на флейте = to play the flute
• играть на барабане = to play the drum / drums

So even though English says play the flute, Russian uses на.

This is just the standard pattern you need to learn with the verb играть when talking about instruments.

Because after играть на meaning to play an instrument, Russian uses the prepositional case.

So the nouns change form:

• флейта → на флейте
• барабан → на барабане

That is why you do not see the dictionary forms флейта and барабан here.

A few similar examples:

• гитара → на гитаре
• скрипка → на скрипке
• рояль → на рояле

So the pattern is:

играть на + prepositional case

А often connects two ideas with a mild contrast or comparison.

Here it means something like:

• while
• whereas
• and ... meanwhile

So:

• Моя подруга играет на флейте, а её брат — на барабане.

means something like:

• My friend plays the flute, while her brother plays the drum(s).

Why not the others?

• и = simple and, just adding information
• но = but, stronger contradiction
• а = contrast or change of topic, often very natural in comparisons

Since the sentence compares what one person plays with what another person plays, а is the best choice.

The dash shows that something has been left out because it is understood.

The full version would be:

• Моя подруга играет на флейте, а её брат играет на барабане.

In the actual sentence, the second играет is omitted:

• Моя подруга играет на флейте, а её брат — на барабане.

This is very common in Russian. The dash helps mark the missing verb and avoids repetition.

So the dash here is not changing the meaning; it is just standing in for the omitted играет.

Её means her.

So:

• её брат = her brother

This is the correct possessive form for a female owner/possessor.

A useful comparison:

• его брат = his brother
• её брат = her brother
• их брат is not correct for their brother; it should be их брат

More importantly, её as a possessive word does not change to match the noun:

• её брат = her brother
• её сестра = her sister
• её друзья = her friends

So unlike мой / моя / моё / мои, the word её stays the same.

Because in Russian, ё is often written as е in normal texts.

So:

• её and ее both mean the same thing here

However, ё is the more precise spelling because it shows the pronunciation clearly.

In learning materials, ё is often written to help students. In native materials, it is very common to see ее instead.

They can sometimes be omitted if the meaning is obvious from context, but here they sound natural and help make the contrast clear.

Compare:

• Подруга играет на флейте, а брат — на барабане.
• Моя подруга играет на флейте, а её брат — на барабане.

The second version is clearer and more specific:

• whose friend?
• whose brother?

Russian does not use possessives as automatically as English in every situation, but in this sentence they are completely natural.

Not necessarily. Барабан is drum in the singular, and на барабане can mean playing the drum in a general sense.

Depending on context:

• на барабане = on the drum / playing drum
• на барабанах = on the drums

If someone specifically means a drum set, the plural can also be used:

• играть на барабанах

But the singular in your sentence is perfectly normal, especially in a simple teaching example.

Because Russian has no articles like English a / an / the.

So Russian simply says:

• на флейте
• на барабане

and context tells you whether English should translate that as:

• a flute
• the flute
• sometimes just flute in a more general sense

This is one of the biggest differences between English and Russian. Russian speakers rely on context, word order, and emphasis instead of articles.

Yes. Russian word order is more flexible than English, although not completely free.

The sentence as written is neutral and natural:

• Моя подруга играет на флейте, а её брат — на барабане.

You could rearrange parts for emphasis, but the original version is the most straightforward for a learner.

For example:

• На флейте играет моя подруга, а на барабане — её брат.

This puts extra emphasis on the instruments.

So yes, Russian word order can change, but the version you have is a very standard, neutral sentence.