W szkole śpiewam w chórze, a Ola gra w orkiestrze.

Because w means in or at, and here it introduces two different places/settings:

• w szkole = at school / in school
• w chórze = in a choir
• w orkiestrze = in an orchestra

Polish often uses w where English might use either in or at, depending on context.

Because after w (when it means location), Polish normally uses the locative case.

So:

• basic form: szkoła = school
• after w: w szkole = at/in school

This is a very common pattern:

• w domu = at home
• w Polsce = in Poland
• w klasie = in the classroom

So szkoła changes to szkole because of the grammar required by w.

For the same reason: after w expressing location or membership in a group/setting, Polish uses the locative case.

So:

• chór → w chórze
• orkiestra → w orkiestrze

English says in a choir and in an orchestra, and Polish uses the same basic idea: w + locative.

Because the verb changes depending on the subject.

• śpiewam = I sing
• gra = she plays

In the sentence:

• (Ja) śpiewam → the speaker is saying I sing
• Ola gra → Ola plays

So the verb endings reflect different persons:

• śpiewam = 1st person singular (I)
• gra = 3rd person singular (he/she/it)

Because in Polish, subject pronouns are often omitted when the verb ending already makes the subject clear.

• śpiewam already means I sing
• You do not need to say ja śpiewam unless you want emphasis or contrast

So this sentence sounds natural without ja.

Compare:

• Śpiewam w chórze. = I sing in a choir.
• Ja śpiewam w chórze. = I sing in a choir. (more emphasis)

In this sentence, a links two ideas with a slight contrast or comparison:

• I sing in a choir, and Ola plays in an orchestra.

Polish a often works like:

• and, when comparing two parallel facts
• sometimes while, whereas, or but, depending on context

Here it suggests a gentle contrast between what I do and what Ola does.

Why not i?

• i is a simple and, used when you are just adding information
• a is very common when two different subjects are being compared side by side

So a Ola gra... sounds very natural here.

It can mean at school in a general sense, not only physically inside the building.

So W szkole śpiewam w chórze can naturally mean something like:

• At school, I sing in the choir

This is often the best way to understand it in English. Polish w szkole is broader than a strictly physical inside the school building interpretation.

Polish word order is more flexible than English word order. This version puts W szkole first to set the scene:

• W szkole = at school
• śpiewam w chórze = I sing in the choir

Starting with W szkole gives a natural context-first feeling: At school, I sing in the choir...

Other word orders are possible, for example:

• Śpiewam w chórze w szkole.
• W chórze śpiewam w szkole.

But they may sound less neutral or shift the emphasis. The original sentence is a very natural, standard way to say it.

Yes, essentially. Polish uses grać for playing a musical instrument and also for performing as part of a musical ensemble.

So:

• grać na gitarze = to play the guitar
• grać w orkiestrze = to play in an orchestra

Notice the difference:

• grać na + instrument = play an instrument
• grać w + group/ensemble = play in a band/orchestra/group

That is why Ola gra w orkiestrze is correct.

The main difference is the ending added by the case change.

• chór = basic form
• chórze = locative form

For an English speaker, the important thing is to notice that -r becomes -rze in spelling, and the ending is pronounced as an extra syllable.

Similarly:

• orkiestra → orkiestrze

These changes are normal in Polish declension, and it is worth learning them as whole patterns rather than trying to translate word by word.

Yes, depending on context. Polish does not have articles like a and the, so the exact English choice depends on the situation.

For example:

• w chórze could mean in a choir or in the choir
• w orkiestrze could mean in an orchestra or in the orchestra

If the speaker means a specific school choir and a specific orchestra already known in context, English might prefer the. If the reference is more general, English might use a. Polish leaves that unstated.