W prezentacji opisuję zdjęcia z wakacji nad morzem.

Because the preposition w meaning in usually requires the locative case when it refers to location.

• basic form: prezentacja = presentation
• after w: w prezentacji = in the presentation

So prezentacji is the locative singular form of prezentacja.

Opisuję is the 1st person singular present tense form of opisywać, which means to describe.

So:

• opisuję = I describe / I am describing

In this sentence, the subject I is not stated separately, because Polish verb endings usually show who is doing the action.

• opisuję already tells you it means I describe

Here zdjęcia is the accusative plural of zdjęcie meaning photo / picture.

It is in the accusative because it is the direct object of opisuję:

• opisuję co? = I describe what?
• zdjęcia = photos

A useful thing to notice is that for many neuter plural nouns, the nominative plural and accusative plural look the same.

• singular: zdjęcie
• plural nominative: zdjęcia
• plural accusative: zdjęcia

So the form does not change here, but the function in the sentence is accusative.

Because the preposition z meaning from requires the genitive case.

The basic dictionary form is:

• wakacje = holidays / vacation

After z, it becomes:

• z wakacji = from the holidays / from vacation

This can feel strange to English speakers because wakacje is grammatically plural in Polish, even when English might use singular vacation.

So Polish often says:

• na wakacjach = on holiday / on vacation
• z wakacji = from holiday / from vacation

In Polish, wakacje is normally a plural-only noun when it means summer holidays / vacation time.

So even if English often says vacation in the singular, Polish usually uses a plural form:

• wakacje były udane = the vacation was successful / the holidays were successful
• jadę na wakacje = I’m going on vacation

This is just something to learn as a vocabulary pattern.

Because nad can take different cases depending on whether there is movement or location.

1. nad + instrumental = location

If something is at / by / over the sea and not moving there:

• nad morzem = by the sea / at the seaside

2. nad + accusative = movement toward

If someone is going to the sea:

• jadę nad morze = I’m going to the seaside

In your sentence, the photos are from holidays by the sea, so this is a location idea, which is why Polish uses nad morzem.

Morzem is the instrumental singular form of morze meaning sea.

• basic form: morze
• after nad for location: nad morzem

So in nad morzem, the noun is in the instrumental case because that is the case used after nad when it means a static location.

No. Polish word order is fairly flexible.

This sentence could also be rearranged, for example:

• Opisuję zdjęcia z wakacji nad morzem w prezentacji.
• Zdjęcia z wakacji nad morzem opisuję w prezentacji.

But the original order:

• W prezentacji opisuję zdjęcia z wakacji nad morzem.

sounds natural if you want to start with the setting in the presentation.

Polish word order often changes the focus or emphasis, not the basic meaning.

Because Polish does not have articles like English a / an / the.

So:

• prezentacja can mean a presentation or the presentation
• zdjęcia can mean photos or the photos

You understand which one is meant from the context.

That is why the Polish sentence does not need separate words for articles.

Yes. The Polish present tense often covers both a simple present and a present continuous meaning in English.

So opisuję zdjęcia can mean:

• I describe the photos
• I am describing the photos

Which translation sounds best depends on context.

This is about aspect, which is very important in Polish.

• opisywać = imperfective
• opisać = perfective

In the present tense, an imperfective verb like opisuję can describe an ongoing or habitual action:

• opisuję zdjęcia = I describe / I am describing photos

A perfective verb does not normally have a true present meaning like that. Its present-tense forms usually refer to the future:

• opiszę zdjęcia = I will describe the photos

So in your sentence, opisuję is used because the speaker is talking about the action as present or ongoing.

It means photos from a holiday/vacation by the sea.

The phrase groups together like this:

• zdjęcia = photos
• z wakacji = from the vacation / holiday
• nad morzem = by the sea

So nad morzem describes the vacation, not the photos directly. In other words, these are photos from holidays spent at the seaside.

A natural English paraphrase would be:

• photos from a seaside vacation
• photos from holidays by the sea