Wymiana ubrań zaczyna się dziś.

Because wymiana (exchange) is followed by a noun in the genitive case.

• ubrania is the nominative plural form: clothes
• ubrań is the genitive plural form: of clothes

So wymiana ubrań literally means exchange of clothes.

A lot of Polish nouns derived from actions, like wymiana (exchange), sprzedaż (sale), naprawa (repair), often take the thing involved in the genitive:

• wymiana walut = exchange of currencies
• naprawa samochodu = repair of a car
• sprzedaż biletów = sale of tickets

ubrania would not work here because it is the wrong case.

Wymiana means exchange or swapping.

In this sentence, it most naturally refers to an event or activity where people exchange clothes, like a clothes swap.

It comes from the verb wymieniać / wymienić, meaning to exchange or to swap.

So:

• wymiana ubrań = clothes exchange / clothing swap

Because clothes in this meaning is usually understood as a plural idea: multiple items of clothing.

In Polish:

• ubranie = a piece of clothing / an outfit / a garment
• ubrania = clothes
• ubrań = of clothes (genitive plural)

So wymiana ubrań refers to exchanging clothes in general, not just one item.

If you wanted to talk about one item, you could say:

• wymiana ubrania = exchange of a garment / changing a garment

But that would usually mean something different from a general clothes swap.

Because zaczyna się is the natural Polish way to say begins / starts for an event, process, or activity.

The verb is zaczynać się = to begin, to start.

So:

• Film zaczyna się o ósmej. = The film starts at eight.
• Lekcja zaczyna się za chwilę. = The lesson starts in a moment.
• Wymiana ubrań zaczyna się dziś. = The clothes swap starts today.

Without się, zaczynać usually means to begin something:

• Zaczynam pracę. = I’m starting work.
• Zaczynam lekcję. = I’m starting the lesson.

So the difference is roughly:

• zaczynać coś = to start something
• zaczynać się = to start / to begin

Not really. In this sentence, się is not best translated literally as itself.

It is a very common Polish particle used in many verbs. Sometimes it is reflexive, but often it is just part of the verb’s normal form.

Here, zaczyna się should be learned as a unit meaning:

• starts
• begins

So although się originally relates to reflexive meanings in many contexts, in this sentence it is better to think of zaczynać się as the standard verb for to begin.

Yes, it can go somewhere else. Polish word order is more flexible than English.

These are all possible:

• Wymiana ubrań zaczyna się dziś.
• Dziś zaczyna się wymiana ubrań.
• Wymiana ubrań dziś się zaczyna. (less neutral, more marked)
• Dziś wymiana ubrań zaczyna się. (possible, but less natural in normal speech)

The sentence you have is very natural and neutral. Putting dziś at the end often gives it a slight focus, like it starts today.

They both mean today.

• dziś = shorter, very common
• dzisiaj = slightly fuller form, also very common

In most situations, they are interchangeable:

• Wymiana ubrań zaczyna się dziś.
• Wymiana ubrań zaczyna się dzisiaj.

dziś can sound a bit more compact or stylistically neat, but both are completely normal.

Because the subject is wymiana, which is a singular noun.

Even though ubrań refers to many clothes, it is not the grammatical subject. It is only part of the phrase wymiana ubrań.

The main noun is:

• wymiana = exchange

And wymiana is:

• feminine
• singular

So the verb must be singular too:

• wymiana ... zaczyna się

Compare:

• Wymiana ubrań zaczyna się dziś. = The clothes swap starts today.
• Ubrania są tanie. = The clothes are cheap.

In the second sentence, ubrania is the subject, so the verb is plural.

Yes, zaczyna się is grammatically present tense.

But in Polish, just like in English, the present tense can be used for a scheduled future event:

• Pociąg odjeżdża jutro o szóstej. = The train leaves tomorrow at six.
• Film zaczyna się wieczorem. = The film starts in the evening.
• Wymiana ubrań zaczyna się dziś. = The clothes swap starts today.

So this is a normal way to talk about planned or scheduled events.

A simple approximation is:

vih-MYA-na oo-BRAHN za-CHI-na shyeh jeesh

A few pronunciation notes:

• wy in wymiana sounds roughly like vih
• ą in ubrań is nasal, but before ń it is often pronounced close to on/om or simply a nasalized vowel, so learners often approximate ubrań as oob-rahn
• cz in zaczyna sounds like ch in chop
• się sounds roughly like shyeh
• dziś sounds roughly like jeesh or dʑiɕ if you know IPA

The stress is normally on the second-to-last syllable:

• wyMIAna
• uBRAŃ
• zaCZYna
• DZIŚ (one syllable)

Yes, but the tone changes.

• ubrań is more neutral and standard
• ciuchów comes from ciuchy, which means clothes in a more informal way, like stuff/clothes or clothes in everyday speech

So:

• Wymiana ubrań zaczyna się dziś. = neutral, standard
• Wymiana ciuchów zaczyna się dziś. = more casual

If this is for an event notice, poster, or announcement, ubrań is usually the better choice.

Normally, no. In this context, wymiana ubrań is understood as exchange of clothes, not putting on different clothes.

If you want to say changing clothes, Polish would usually use something like:

• przebieranie się = changing clothes
• zmiana ubrań = change of clothes / changing clothes, depending on context

So wymiana ubrań strongly suggests a swap/exchange, not changing what you are wearing.

Yes. It is short, complete, and very natural, especially in announcements, posters, social media posts, or event descriptions.

It sounds like something you might see in:

• an event listing
• a school notice
• a community center announcement
• a message about a clothes swap event

Because Polish often allows short subject + verb + time sentences, this works perfectly well on its own.