Nasza solistka założy nowy kostium przed występem.

Here założy means will put on or will wear/put on for the occasion, referring to clothing.

The verb is założyć, which often means:

• to put on clothes, shoes, glasses, jewelry, etc.
• in other contexts, it can also mean things like to found, to assume, or to put/place, but here it is clearly about clothing because of nowy kostium.

So in this sentence, it means that the soloist will put on a new costume before the performance.

This is a very common Polish question. Założyć is a perfective verb, and perfective verbs do not normally have a true present tense. Their “present-looking” forms are used to talk about the future.

So:

• zakłada = is putting on / puts on (imperfective, present)
• założy = will put on (perfective, future)

That means:

• Nasza solistka zakłada nowy kostium = Our soloist is putting on / puts on a new costume
• Nasza solistka założy nowy kostium = Our soloist will put on a new costume

The perfective form suggests a single completed action: she will get dressed in that costume before the event.

Because solistka is a feminine noun.

In Polish, possessive adjectives like nasz (our) must agree with the noun in:

• gender
• number
• case

Since solistka is:

• singular
• feminine
• nominative

the correct form is nasza.

Compare:

• nasz solista = our male soloist
• nasza solistka = our female soloist

Solistka means female soloist.

It is the feminine form of:

• solista = male soloist (or sometimes a soloist in a more general sense, depending on context)
• solistka = specifically feminine

The ending -ka is a common way to form feminine nouns in Polish.

Because kostium is a masculine inanimate noun, and here it is the direct object of the verb założy.

With masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: nowy kostium
• accusative: nowy kostium

That is why the sentence uses nowy kostium.

Why not the other forms?

• nowego kostiumu is not right here because that would be a different case pattern, not the one needed for this direct object.
• nowa kostium is wrong because nowa is feminine, while kostium is masculine.

Because przed often requires the instrumental case.

So:

• basic form: występ = performance
• after przed: przed występem = before the performance / before a performance

This is a standard pattern:

• przed koncertem = before the concert
• przed obiadem = before lunch
• przed spotkaniem = before the meeting

The ending -em is a typical instrumental singular ending for many masculine nouns.

Very often, yes, but it depends on meaning.

With przed meaning in front of or before, it commonly takes the instrumental:

• przed domem = in front of the house
• przed występem = before the performance

So in your sentence, przed występem is exactly what we expect.

No. Przed występ is ungrammatical here.

After przed, you need the correct case form, which is instrumental:

• correct: przed występem
• incorrect: przed występ

Polish prepositions usually force a specific case, so this is something learners need to memorize.

No, Polish word order is relatively flexible, although some orders sound more natural than others.

The neutral order here is:

• Nasza solistka założy nowy kostium przed występem.

But you could also say:

• Przed występem nasza solistka założy nowy kostium.
• Nowy kostium nasza solistka założy przed występem.

These variations change the focus or emphasis, not the basic meaning.

For example:

• Przed występem... emphasizes the time.
• Nowy kostium... emphasizes what she will put on.

This is mainly a question of aspect.

• zakłada comes from zakładać (imperfective)
• założy comes from założyć (perfective)

In this context:

• zakłada nowy kostium
  = she is putting on a new costume / she puts on a new costume
  This focuses on the process, habit, or repeated action.

• założy nowy kostium
  = she will put on a new costume
  This focuses on a single completed action in the future.

So the sentence uses założy because it is talking about one future event before the performance.

Because Polish has no articles like a or the.

Whether występem means:

• before a performance
• before the performance

depends on context.

The same is true for many Polish nouns. Learners coming from English often look for an article, but Polish simply does not use one.

In modern Polish, ł is pronounced roughly like English w.

So:

• założy is pronounced approximately za-WO-zhy
  where ż sounds like the s in measure

Very roughly:

• za = like za in bizarre but shorter
• ło = like wo
• ży = like zhih / zhy

So założy sounds roughly like za-wo-zhy.

Not always. Kostium can mean different kinds of costume or outfit depending on context.

It can refer to:

• a stage costume
• a costume for performance or theater
• sometimes a more formal or specific outfit, depending on context

In this sentence, because we have solistka and przed występem, the intended meaning is very naturally a performance costume.