Na wesele kuzynki założę elegancki garnitur, bo zwykła bluza nie pasuje do takiej uroczystości.

Because na can take different cases depending on the meaning.

Here it means to / for a wedding event, so it expresses direction or destination, and that requires the accusative: na wesele.

Compare:

• Idę na wesele = I’m going to a wedding
• Jestem na weselu = I’m at a wedding

So:

• na wesele = motion toward an event / purpose
• na weselu = location, being there

Kuzynki is the genitive singular of kuzynka (female cousin).

In wesele kuzynki, the genitive shows possession or connection:

• wesele kuzynki = my cousin’s wedding / the wedding of my cousin

This is a very common Polish pattern:

• samochód brata = brother’s car
• dom rodziców = parents’ house
• ślub siostry = sister’s wedding

So kuzynki tells you whose wedding it is.

Yes. Kuzynka means female cousin, and kuzyn means male cousin.

So:

• wesele kuzynki = the wedding of a female cousin
• wesele kuzyna = the wedding of a male cousin

English uses just cousin for both, but Polish normally marks the gender.

Polish often leaves out possessive words like my, your, his, etc. when the meaning is already clear from context.

So:

• Na wesele kuzynki założę... naturally means I’ll wear ... to my cousin’s wedding
• If needed for emphasis or clarity, you could say mojej kuzynki

Both are possible:

• na wesele kuzynki
• na wesele mojej kuzynki

The version without mojej is very natural.

Literally, założę is closer to I will put on. In context, though, it often corresponds to English I’ll wear.

The verb założyć is perfective, so założę refers to a completed future action:

• Założę garnitur = I’ll put on a suit / I’ll wear a suit

Polish often uses założyć when talking about what clothes someone chooses for an occasion.

A useful contrast:

• zakładać / założyć = to put on
• nosić = to wear in general, habitually
• mieć na sobie = to have on, to be wearing

So in this sentence, założę is the natural choice because it is about a specific future occasion.

That happens because założyć is a perfective verb.

In Polish, perfective verbs do not have a normal present tense. Their present-looking forms actually refer to the future:

• zrobię = I will do
• napiszę = I will write
• założę = I will put on / wear

So założę is formally shaped like a present-tense form, but its meaning is future.

Because garnitur is a masculine inanimate noun, and here it is the direct object of założę, so it is in the accusative.

For masculine inanimate nouns, the accusative singular is usually the same as the nominative:

• nominative: elegancki garnitur
• accusative: elegancki garnitur

That is why nothing changes here.

The adjective must agree with the noun:

• elegancki matches garnitur in gender, number, and case

Because zwykła bluza is the subject of the clause:

• zwykła bluza nie pasuje... = an ordinary sweatshirt doesn’t suit...

Subjects are in the nominative, so:

• zwykła bluza = nominative singular

If it were a direct object, then you would use the accusative:

• Mam zwykłą bluzę = I have an ordinary sweatshirt

So the form depends on its role in the sentence.

The verb pasować do means to suit, to go with, or to be appropriate for.

This verb requires do + genitive:

• pasować do czegoś = to suit something

So:

• do uroczystości = for / to an occasion
• do takiej uroczystości = for such an occasion

Examples:

• To nie pasuje do sukienki = That doesn’t go with the dress
• Jeansy nie pasują do tej restauracji = Jeans aren’t suitable for that restaurant

You just need to learn pasować do as a fixed pattern.

Because do requires the genitive, and both words must match that case.

Base forms:

• taka uroczystość = such an occasion

After do, they become genitive singular:

• takiej uroczystości

This is adjective-pronoun agreement:

• taka → takiej
• uroczystość → uroczystości

So the phrase literally follows the grammar of do + genitive.

Both can mean because, but bo is more common and conversational.

• bo = everyday, natural in speech
• ponieważ = a bit more formal or written

So:

• Założę elegancki garnitur, bo... sounds very natural
• Założę elegancki garnitur, ponieważ... is also correct, just slightly more formal

Polish usually drops subject pronouns when the verb ending already shows who is doing the action.

Here:

• założę already means I will put on / wear

So ja is unnecessary unless you want emphasis:

• Założę elegancki garnitur = I’ll wear an elegant suit
• Ja założę elegancki garnitur = I will wear an elegant suit

English needs the pronoun, but Polish often does not.

Yes. Polish word order is more flexible than English because case endings show grammatical roles.

The given sentence is natural:

• Na wesele kuzynki założę elegancki garnitur, bo zwykła bluza nie pasuje do takiej uroczystości.

But other versions are possible, with slightly different emphasis:

• Założę elegancki garnitur na wesele kuzynki, bo zwykła bluza nie pasuje do takiej uroczystości.
• Bo zwykła bluza nie pasuje do takiej uroczystości, na wesele kuzynki założę elegancki garnitur.

Putting Na wesele kuzynki first emphasizes the occasion: as for my cousin’s wedding...

It can mean something between ceremony, formal occasion, and important event, depending on context.

In this sentence, taka uroczystość means something like:

• such an occasion
• such a formal event
• such a ceremony

It suggests that a wedding is a special, dressy occasion, so an ordinary sweatshirt is not appropriate.